Endian changes since formal review

• Both the endian types and endian conversion functions now support 32-bit (float) and 64-bit (double) floating point, as requested.
• Both the endian types and endian conversion functions have been renamed, using a naming pattern that is consistent for both integer and floating point, and that emphasizes that aligned types are usually preferred compared to unaligned types.
• The conversion.hpp conversion functions have been much revised, refactored, and otherwise improved based on review comments.
  • UDT's are supported, as requested.
  • Both return-by-value and modify-in-place interfaces are provided, as requested.
  • 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, as requested.
• Compiler (Clang, GCC, VisualC++, etc.) intrinsics and built-in functions are used in the implementation where appropriate, as requested.
• For the endian types, the implementation uses the endian conversion functions, as requested.
• Headers have been renamed to endian/types.hpp and endian/conversion.hpp. Infrastructure file names changed accordingly.
• C++11 features such as noexcept are now used, while still supporting C++03 compilers.
• Acknowledgements have been updated.
• Headers have been reorganized to make them easier to read, with a synopsis at the front and implementation following, as requested.