Add .gitignore file

Add a gitgnore file, and set it to ignore all .pyc files
since we don't need these in the repository
Tidy ingestion docstrings and update web docs

Tidy up the docstrings in the ingestion routines so that they
work properly with sphinx.

Add ingest_images, ingest_images_geo_tools and ingest_images_file_readers
to the documentation page.