add isoweek extractor to extract the ISO8601 week.
add isoweek accessor test for a tricky date
Couple of changes based on hadley's suggestions on my pull request
add fasttime support for POSIX formats
adjust posix regexp to avoid passing ISO8601 to fasttime
add modified tparse.c from fasttime package
add backup and dll files to gitignore
white-space cleanup
add fasttime description to docs
add commented speed tests
parse_date_time returns POSIXct

    Makes parsing way faster for fasttime POSIX. It was also documented
    as such but not honored.
explicit force_tz is needed when fastPOSIXct is used
add C level parse_hms for fast (and correct!) hms/ms/hm parsing
R interface to hms/ms/hm C code + docs + tests
NAMESPACE useDynLib adjustment
add Simon Urbanek to contributors
comment C function pare_hms
add R level wrapper .parse_hms
incorporate Hadley's style comments
makes olson_time_zones() more OS-agnostic

Should work for Ubuntu, as well as Windows. Other OS easy to account for, just to specify file location for `zone.tab`.

Tests included