Fixed handling of duplicated form inputs
Do not add forms inputs without name to payload
Updated documentation for Eso package.
Minor sphinx improvement.
Added help option to Eso.instrument_query()
Improved Eso.query_instrument() interface.

Using `columns` and `column_filters` keywords instead of the generic
`**kwargs`.
Improved help for query_instrument()

A checkbox looking like `[ ]` now shows which columns can be
controlled. The default columns in the output are ticked like `[x]`.
Added beautifulsoup4 dependency.
Added beautifulsoup4 to .travis.yml
Small docstring update to instrument_query()
Updated eso package documentation
Merge pull request #314 from jwoillez/form_fix

Some fixes to the way forms are handled in the Eso package