Added Thai pron extraction

[lfashby]

Added tha.py to extract directory. It is almost identical to khm.py, the only difference is in the _IPA_XPATH variable, which oddly enough, can be set to the same value as IPA_XPATH in default.py. The difference between tha.py and default.py is that we don't want to use _yield_phn for tha.py as we want to skip the for pron_xpath in request.html.xpath(config.pron_xpath_selector): step in _yield_phn and just go straight to calling the core yield_pron function.
I suppose I could import IPA_XPATH from default.py into tha.py if that would make more sense?

I'm checking in the Thai data as well, it's our first data collected using the new 'segments' package parsing.

I also changed logging in scrape.py to just log messages from within scrape.py (as well as a few changes I noticed should be made running the big scrape).

[jacksonllee]

Yay for Thai!

If we close #71 after this PR is merged, should we open another ticket for adding the --no-tone flag in the future? (I agree with Kyle that we don't need to work on this feature now.)

I suppose I could import IPA_XPATH from default.py into tha.py if that would make more sense?

+1 for using IPA_XPATH from default.py instead. (We can think about how to refactor things further later.)

[jacksonllee]

Sorry I forgot this -- please add an entry to CHANGELOG.md for handling Thai.

[lfashby]

+1 for having a general --no-tone ticket.

The changelog entry is basically the same as Khmer's, I couldn't think of anything more creative.

[jacksonllee]

LGTM! Please use the "squash and merge" option for merging.

Just open #91 for the "no tone" flag.