Create Riverscapes XML Pip module

[MattReimer]

The task: Pull all simple common modules out of riverscapes-tools and create a pip module for writing XML files

• [ ] CI versioning and publishing to PyPi
• [x] Unit tests
• [x] XML writing
• [ ] Validation 2 ways (validate XML and validate project)
• [ ] Documentation

[MattReimer]

FYI @sdunesme

[MattReimer]

good progress here. Nothing tested or published yet but I gave some nice patterns for creating projects

Also I plan on writing lots of examples and more as people ask questions:

https://github.com/Riverscapes/RiverscapesXML/blob/python-lib/python/packages/rsxml/examples/project.py