v3.0.0

This release makes Windows builds a bit more flexible and reliable, in preparation for putting out a conda package for pyscamp.

There are some backwards incompatible changes made from the previous release:

1. pyscamp requires cmake 3.15 or greater now (up from 3.12). Most users should have a much more recent version of cmake anyway so this shouldn't be too big an issue.
2. Some changes were made to how to specify environment variables to set compilers/generators for SCAMP and pyscamp, overall this should be more aligned with the normal usage of cmake. Documentation has been updated to reflect these changes.

What's Changed

• Clean up pyscamp build logic in setup.py by @zpzim in #96

Full Changelog: v2.1.3...v3.0.0