The temporary values created during subtensor broadcast-value computations would
cause the test value computation steps to complain/err.  This change prevents
that.

This change also fixes the `set_subtensor` boolean gradient bug in #105.

This change prevents downstream code (e.g. test value computation) from throwing
exceptions (e.g. `ValueError`s) that break the logic in
`theano.tensor.basic.as_tensor_variable`.

- Fix `*Subtensor*` `Op` shape inference
- Make `theano.tensor.basic.as_tensor_variable` consistent in how it handles constant conversions
- Remove `TensorConstant` caching

Now, when `as_tensor_variable` is given `Constant` types, it will return the
same result as a call with the underlying non-`Variable` data.

Closes #98

Closes #99

The merge-based functions were moved to `toolbox` to reduce unnecessary
cross-module dependencies (especially among core modules).  `equal_computations`
was moved from `scan_module` because it provides a basic graph object `__eq__`
implementation and it has multiple references outside of its own
module/sub-package.

Combining checks into one and dealing with skipped runs

* Update README

* Remove unused/unnecessary build and project files

* Update the issues template

* Add a pull request template
Co-authored-by: Brandon T. Willard <brandonwillard@users.noreply.github.com>
Co-authored-by: Thomas Wiecki <thomas.wiecki@gmail.com>

Stop importing test suite from __init__