Add proxy/port to configuration
correct remarks from #481
implement remarks for #481, also add scheme as requested in #472
correct default port config for proxy and deserialize function
Change docs license to Apache License, Version 2.0

I've looked through all contributions to the docs. Any contributions not by
Thomas Adamcik or myself are trivial (e.g. typo fixes) or have mostly been
replaced by later changes. Thus I'm comfortable with changing the license with
the agreement of Thomas Adamcik.

By changing the documentation license to be the same as the source code
license, we avoid ambiguities around the license of e.g. docstrings which are
written as part of the source code but are included in the generated docs.
String config value can be optionnal AND have a choices list
Integer value can be optionnal
add some tests about optionnal integer and optionnal+choices string
Correct typo
Merge pull request #481 from AlexandreP2101/develop

Improve proxy support by adding port and scheme to config.