transaction user and description: text above, bytes below

Also added _s to _transaction_meta_data_text_variables and
_text_transaction_info to mark them as private.

Conflicts:
	CHANGES.rst

WRT travis and winbot.

Conflicts:
	doc/guide/transactions-and-threading.rst

for user_name and description

Cleaned up check_checkCurrentSerialInTransaction

Weird, I thought I'd tested the transaction changes against ZODB. :/

- Use assertEqual rather than assertTrue for better error messages.

- Fixed a typo that caused an assertion to be missed.

Fix a few typos in documentation

Add a Gitter chat badge to README.rst

Remove obsolete code

They haven't been used in a long time.

2.6 is unsupported. 2.6 is long unsupported.

Consistently spell the version checks that remain as PY2 or PY3 to make
them slightly easier to find.

Enable using coverage and coveralls for coverage reporting.

Set this up on travis.

This was just slightly tricky because of the use of 'j99' in the call to
bin/test.