Endian changes since formal review

• Headers rename to endian/types.hpp and endian/conversion.hpp. Infrastructure file names changed accordingly.
• The conversion.hpp conversion functions have been much revised, refactored, renamed and otherwise improved based on review comments.
  • UDT's are supported.
  • float(32-bits) and double (64-bits) are supported.
  • Both return-by-value and modify-in-place interfaces are provided.
  • Synonyms for the BSD byte swapping function names popularized by OS X and Linux are provided, so that that developers already used to these name can continue to use them if they wish.
  • In addition to the fixed endianness functions, functions that perform compile-time (via template) and run-time (via function argument) dispatch are now provided.
• Compiler (Clang, GCC, VisualC++, etc.) intrinsics and built-in functions are used in the implementation where appropriate.
• For the aligned endian integer types, the implementation uses conversion.hpp conversion functions.
• C++11 features such as noexcept are used, while still supporting C++03 compilers.
• Acknowledgements have been updated.
• Headers have been reorganized to make them easier to read, as requested, with a synopsis at the front and implementation following.