return byte slice directly from buffer

Updates #52
optimized buffer refill

No extra allocation when refilling the buffer
Closes #52
getSystemVar result validity doc
Optional DATE / DATETIME to time.Time parsing

Closes #9
Update README.md
factored common initialization code out
added time test (broken)
added allow_invalid_dates to dsn in time test (still broken)
improved structure (but still broken)
missed a truncate, tests pass now
drop collation statements in create, drop charset in create where not text
applied most change requests (missing err handling in Scan)
readded fail
removed line breaks
Merge pull request #57 from arnehormann/master

refactoring of driver_test.go
Add strict mode

Closes #40
fix readme fmt
Close rows on error
Make warning details accessible

Makes the details of MySQLWarnings accessible through an exported struct
clean up test