Algebra-with-sympy

- BUG FIX accommodate empty re.search results in preparser. Prevents unnecessary error messages.

- Setting integers as exact (set_integers_as_exact(), the default) now only sets integers as exact within Sympy and Algebra_with_Sympy expressions. This increases compatibility with other packages that depend on integers being Python integers.
- Refuse to import Algebra_with_Sympy if an incompatible version of Sympy is installed in the environment.
- Added warning explaining how to install a compatible version of Sympy.

Mostly minor bug fixes. See [Change Log](https://gutow.github.io/Algebra_with_Sympy/algebra_with_sympy.html#change-log).
Also available via pip: `pip install Algebra-with-SymPy`.

First Stable Release:

- A few bug fixes and updates to functionality. See https://gutow.github.io/Algebra_with_Sympy/algebra_with_sympy.html#change-log.
- Also available via pip: `pip install Algebra-with-SymPy`.