Pybald

- Update SQLAlchemy dependency to 1.3.3 to mitigate a
security issue with SQLAlchemy verstions <= 1.3.0

- Update dependencies: WTForms, alembic, SQLALchemy, WebOb
- Change docs from ReStructured text to Markdown

- Fix Python 3 compatibility issue in Proxy.\_\_dir\_\_

- Fix bug with stacktrace template for default Error handler
- Improve the context model binding function

- **Warning** - this release may not be compatible with previous
pybald releases *if* you were making use of the asset pipeline
(bundles, bundle filters, JSX compilation), utilizing the celery
loader or the newrelic adapter
- This removes the webasset pipeline from core pybald. The webasset
pipeline was only used in a few projects and added complexity and
numerous requirements to pybald.
- The webasset pipeline will be re-designed and released as a
supporting pybald package instead of included in the core.
- The newrelic adapter and celery support code will also be
re-designed and released as supporting pybald packages instead of
included in the core.
- This release also bumps the supporting library versions: Mako,
SqlAlchemy, WTForms
- Remove requirement for forked routes library, required behaviors
have been included in the main routes project
- Improve tests and test coverage

- Fix a bug with the default error controller. Now the raw exception
can be passed in and the order of the arguments was changed but not
updated in the default.