Initial commit buffers.hpp and related infrastructure. A separate buffer class without arithmetic operators was requested during the formal review.
Re-implement the endian types by inheriting from endian_buffer.
Add use_cases.cpp
Remove "operator value_type() const noexcept" from buffers. Make the buffer ctor explicit. Buffers were requested by people who do not want automatic conversions because they want full control over conversions, and are very concerned about "efficiency".

Add "operator value_type() const noexcept" to the endian arithmetic types. These types are used by people who do want fully automatic conversions. The arithmetic types need to be drop-in replacements for the built-in arithmetic types for these users.
Major renaming.  Class "endian" becomes class "endian_arithmetic" to mimic the C++ standard's description of such types as "arithmetic types". Rename header accordingly. The convenience typedefs have been changed shorten aligned names, as they are often being, but keeping the unaligned type names relatively short via a simple "_ut" suffix.
Preliminary doc changes to reflect addition of buffers.
Rename the conversion functions to discourage unthinking use of the in-place versions as these are unsafe in that they effectively break the type system by treating the buffer as an undescriminated union. Remove the synonym functions based on names popularized by BSD, OS X, and Linux since these are permitted to be implemented as macros, which would cause endless difficulties if encountered.
Rename endian_buffer typedefs. New names a bit longer, but also a bit more explicit and more obviously related to endian_arithmetic typedefs.
Rework conversion.hpp: Make the UDT customization point for the value returning conversion functions much more explicit. Provide a separate UDT customization point for the in-place conversion functions, and reverse_in_place() overloads for the built-in arithmetic types. Eliminate the unsafe general-use reverse functions. With explicit customization points these are no longer needed. Complete the renaming of conversion functions started in the prior commit. The reverse and reverse_in_place names are much more meaningful and less likely to be misunderstood. The longer "reverse_in_place" name will hopefully at least slow users down before inappropriate (and possibly unsafe use, such as when trying to recover data after an exception).
Add "_endianness" to the names of the two customization points. These names must be defined in user namespaces (for ADL to work) and so must be much more explicit than names that are defined in namespace endian.
More conversion.hpp fixes. Some, but not all, conversion_test tests passing.
Finish conversion.hpp cleanup after name changes. conversion_test.cpp return-by-value tests reorganized and passing. UTD and in-place tests still to come. Add doc/bikeshed.txt to keep record of naming rationale.
Add full set of modify in place tests.
UDT tests added. Passing on Windows, all local compilers.
Finalize buffer and arithmetic decomposition. Finalize name changes. Finalize test cases. Remove cruft. Docs still to do.
Add conversion_use_case
Doc tweeks.
Tweak comments.
Current very unstable state.
Work-in-progress on endian_buffer docs.