support microseconds with MySQL 5.7+

passes all tests except TIME(1) -> string in binary protocol.
TIMESTAMP support with microsecond resolution is still incomplete.
all tests passing
PR done, all tests succeed and problematic ones are auto-skipped
Oh Travis, why have you forsaken me (sorry dear watchers)
faster and unified date formatting, flexible lengths, better tests
trying to get more information out of Travis
trying to get more information out of Travis II
skip offending test on misbehaving servers
skip offending test on misbehaving servers - another way
improved date formatting with inspiration from strconv
changes based on review
replace panic with error, handle missing error case
removed TIMESTAMP tests (still tested in TZ conversion)
added new TIMESTAMP test
Merge pull request #249 from arnehormann/microsecs

Microseconds