solve bug the "z" format bug #150
add tests for "z" formatting
parsers documentation cleanup
remove ymdThms,  (it is confusing, not needed, and was not working :)
simplify parse_date_time (the minuscule gain in speed is not worthwhile the obfuscation of the code)
rename .get_locale_regs into .build_locale_regs, because this is what it does
rearange and document the code in guess.r
Make %z format recognize (Z|-0800|-08|-08:00) ISO8601 standard ofsets.

 Also add support for pre-processing formats and date-strings before
parsing. Add support for multi-letter formats and add new lubridate offset
formats %OO, %Oo,%Ot to support ISO8601.
more documentation of gueser code
rename Ot format into Ou. Stands for UTC identifier (aka zulu time).
add tests for new iso8601 parsing
remove ymdThms reference from the documentation, roxeginize didn't work, so did it manually.
lubridate_formats is used only in stamp. Rearange and update documnetation. Do not export.
add xxxTz format to xxx_hms function to capture ISO8601
reindent with 2 spaces to complly with lubridate style
slight code rearangements in guess.r
correct regexp for OO format
move the place of unique
don't limit warnings if length(x) < 10, inconsistent and ugly
add tests for ISO8601 xxx_hms