Unify extension's and fortran-language-server's interface

[gnikit]

Use json file parse settings to the extension similar to C++. The idea is to use that same json file to parse options to fortls. For that we will have to rewrite fortls to allow such flexibility.

[gnikit]

This would also make trivial to solve #133

[gnikit]

I have already added the base for this work by making VS Code watch .fortls and settings files. What we would now need is to either use the language server configure file or create a new one where the VS Code settings for building, linting, (server resolution possibly) will be stored.