Pyramid-sqlassist

* mypy support
* drop py2-py35
* removed the `in_progress` namespace. unplanned.

* New Requirements:
* SqlAlchemy > 1.4.7
* [testing] ZopeSqlAlchemy > 1.6
zope.transaction does not work with the 1.4-1.4.6 of SqlAlchemy
* Drop Python3.5; add Python3.9

* packaging fixes

* support for `transaction` is slightly altered. this package will now raise
an import error if `transaction` and `zope.sqlalchemy` are not available IF the
environment variable `SQLASSIST_DISABLE_TRANSACTION` is not set.
* cleaned up docstrings
* packaging fixes
* excluding SQLAlchemy==1.4 branch until further testing can be done. this will return soon.

* packaging fixes

* now requires:
zope.transaction >= 1.2
sqlalchemy >= 1.3