Problem: Some time related functions cannot be used without linking
the entire server.

Solution: Move time functions which do not depend on the server to mysys.

In detail:

- Only report warnings through THD from functions with the _with_warn suffix
- Change include guard to new standard
- Move functions not used externally from header to my_time.cc
- Default initialization for MYSQL_STATUS members
- Group function declarations
- Change macros to inline functions
- Removed linking of sql_time.cc.o into binlog client
- Converted legacy comments to Doxygen
- Added Doxygen comments to undocumented exported functions
- Make globals const where possible
- Add sanity checks for shift operations in my_packed_time_ functions
- Add unit test for my_time
- Remove unused function parse_date_time_format()
- Move known_date_time_formats[] to item_timefuncs.cc

Change-Id: I283e1f9add9ab96b407955b472d6f4b795e1d368