[WIP] Change default location for config files to platform defined config folder (Close #42)

[cjbassi]

This change makes wpm load and store config files to ~/.config/wpm by default, specifically the wpm.csv and wpmrc files. It also removes the current functionality of loading config files from the home directory, but let me know if I should readd that functionality as a fallback if the ~/.config/wpm/* files don't exist since this would be a breaking change otherwise.

[cslarsen]

The PR itself is fair enough, but does indeed break a lot for existing, casual users (myself included). If I'd merge this, then it would not read my current settings or stats.

I think you need an upgrade strategy in the PR, where you copy the files over. Also, make sure .config exists. I am not too deep into the XDG specs, but if you can help me out understanding how this is useful (and provide an automatic switchover functionality) then I'd merge this PR.

[cjbassi]

Yah, breaking changes should definitely be avoided. I think the best solution would be to readd support for the currently used config file paths in this PR and default to that if the ~/.config/wpm/* files don't exist. So we're just creating a hierarchical lookup for the config file paths, which is a pretty standard cli app feature actually.

Also, the OSX standardization would need to be added to this PR, as mentioned in #42.