Update API documentation to reflect current contents

[kinverarity1]

The API documentation is probably not including some new or renamed functions, and perhaps includes some unused ones. Needs updating.

https://lasio.readthedocs.io/en/latest/lasio.html

https://github.com/kinverarity1/lasio/blob/master/docs/source/lasio.rst

[dcslagel]

@kinverarity1, Is there anything I've missed updating in the document pull-request earlier in the year that should be updated in the API documentation?

Thanks!, DC

[dcslagel]

I'm not sure if this is done now, but I've removed myself as the assignee for the time being.