docs: Update docs to reflect current functions

[lsetiawan]

Updates the documentations for current functions. This includes tweaks to the api.rst to automatically create API Documentation from docstrings.

Additionally, the following changes has been made:

• config.rst: Added posfilter and transponders modules
• dataspec.rst: Added data specification v1
• noxfile.py: Added a docs session with separated setup and build step
• readthedocs: Updated rtd to use nox for setting up docs