Standardize header names and file locations

This is both a really big and a really small commit. It is small in
that it only contains renaming, moving and modification of include
directives caused by this.

It is really big in the obvious way of touching something like 200
files.

The new rules for naming files is simple: headers use the `.hpp`
extension. The rules for physical file layout is still kinda in
progress, but the basics are also simple:
 * Significant parts of functionality get their own subfolder
   * Benchmarking is in `catch2/benchmark`
   * Matchers are in `catch2/matchers`
   * Generators are in `catch2/generators`
   * Reporters are in `catch2/reporters`
   * Baseline testing facilities are in `catch2/`
 * Various top level folders also contain `internal` subfolder,
   with files that users probably do not want to include directly,
   at least not until they have to write something like their own
   reporter.
    * The exact files in these subfolders is likely to change later
      on

Note that while some includes were cleaned up in this commit, it
is only the low hanging fruit and further cleanup using automatic
tooling will happen later.

Also note that various include guards, copyright notices and file
headers will also be standardized later, rather than in this commit.

src/catch2/catch_stringref.hpp

@@ -0,0 +1,114 @@
+/*
+ *  Copyright 2016 Two Blue Cubes Ltd. All rights reserved.
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+#ifndef CATCH_STRINGREF_H_INCLUDED
+#define CATCH_STRINGREF_H_INCLUDED
+
+#include <cstddef>
+#include <string>
+#include <iosfwd>
+#include <cassert>
+
+namespace Catch {
+
+    /// A non-owning string class (similar to the forthcoming std::string_view)
+    /// Note that, because a StringRef may be a substring of another string,
+    /// it may not be null terminated.
+    class StringRef {
+    public:
+        using size_type = std::size_t;
+        using const_iterator = const char*;
+
+    private:
+        static constexpr char const* const s_empty = "";
+
+        char const* m_start = s_empty;
+        size_type m_size = 0;
+
+    public: // construction
+        constexpr StringRef() noexcept = default;
+
+        StringRef( char const* rawChars ) noexcept;
+
+        constexpr StringRef( char const* rawChars, size_type size ) noexcept
+        :   m_start( rawChars ),
+            m_size( size )
+        {}
+
+        StringRef( std::string const& stdString ) noexcept
+        :   m_start( stdString.c_str() ),
+            m_size( stdString.size() )
+        {}
+
+        explicit operator std::string() const {
+            return std::string(m_start, m_size);
+        }
+
+    public: // operators
+        auto operator == ( StringRef const& other ) const noexcept -> bool;
+        auto operator != (StringRef const& other) const noexcept -> bool {
+            return !(*this == other);
+        }
+
+        auto operator[] ( size_type index ) const noexcept -> char {
+            assert(index < m_size);
+            return m_start[index];
+        }
+
+        bool operator<(StringRef const& rhs) const noexcept;
+
+    public: // named queries
+        constexpr auto empty() const noexcept -> bool {
+            return m_size == 0;
+        }
+        constexpr auto size() const noexcept -> size_type {
+            return m_size;
+        }
+
+        // Returns the current start pointer. If the StringRef is not
+        // null-terminated, throws std::domain_exception
+        auto c_str() const -> char const*;
+
+    public: // substrings and searches
+        // Returns a substring of [start, start + length).
+        // If start + length > size(), then the substring is [start, start + size()).
+        // If start > size(), then the substring is empty.
+        constexpr StringRef substr(size_type start, size_type length) const noexcept {
+            if (start < m_size) {
+                const auto shortened_size = m_size - start;
+                return StringRef(m_start + start, (shortened_size < length) ? shortened_size : length);
+            } else {
+                return StringRef();
+            }
+        }
+
+        // Returns the current start pointer. May not be null-terminated.
+        constexpr char const* data() const noexcept {
+            return m_start;
+        }
+
+        constexpr auto isNullTerminated() const noexcept -> bool {
+            return m_start[m_size] == '\0';
+        }
+
+    public: // iterators
+        constexpr const_iterator begin() const { return m_start; }
+        constexpr const_iterator end() const { return m_start + m_size; }
+    };
+
+    auto operator += ( std::string& lhs, StringRef const& sr ) -> std::string&;
+    auto operator << ( std::ostream& os, StringRef const& sr ) -> std::ostream&;
+
+    constexpr auto operator "" _sr( char const* rawChars, std::size_t size ) noexcept -> StringRef {
+        return StringRef( rawChars, size );
+    }
+} // namespace Catch
+
+constexpr auto operator "" _catch_sr( char const* rawChars, std::size_t size ) noexcept -> Catch::StringRef {
+    return Catch::StringRef( rawChars, size );
+}
+
+#endif // CATCH_STRINGREF_H_INCLUDED