[RFC] change directory structure

[IonBazan]

Moving all source files into src directory makes it easier to search trough the code since there is no need to exclude vendor dir all the time. Let me know what are your thoughts.

Warning: please note that Tests directory has been renamed to lowercase tests which might not be supported on some systems. You may need to rename it manually after checking out this branch.

[malarzm]

@alcaeus I remember we were talking about this transition at least few times before, were we just procrastinating doing so or was there something different? I recall the argument about rebasing open PRs, but given there are just 4 other so it's not that important :)

[franmomu]

I'm 👍, if it's because of the open PRs it not a big deal right now I think

[stale[bot]]

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