Rewrite parse_time so it understands time zones and microseconds

[Zverik]

Fixes #83, #114 and #148.

I decided to go with a precompiled regular expression. It should be fast, since there are no + or * special characters in it. Tested in Python 2.7 and 3.6.

[coveralls]

Coverage increased (+0.09%) to 85.612% when pulling 9d89f9a on Zverik:fix_tz_and_micro into b9219a9 on tkrajina:master.

[coveralls]

Coverage increased (+0.003%) to 85.524% when pulling c9d5b3a on Zverik:fix_tz_and_micro into 5358e8c on tkrajina:master.

[christianhauff]

Any progress on this PR? I just spent an hour on a timezone problem before I realized that gpxpy just ignores the timezone information.

[bstadlbauer]

Would it be possible to merge and release this as some point? Would be really helpful to support time zones 👍

[tkrajina]

Yes, I plan to merge this pull request. Before diving in the code @Zverik do you think this is now the final version or you have more things to commit here?

[Zverik]

I think that's final: it's on par with the version we use in our company.

[bstadlbauer]

Thanks for merging and releaseing!