I know formatting commits suck... And I try to avoid them.

But this commit was absolutely necessary... The coding style in this
program was not ok and not the same over the whole program.

The commit is hard to read, but this is what I changed:
- Tabs for indentation instead of spaces
- Same style over the whole program (suckless style)

- Better README.md
- Headlines in all files
- CONTRIBUTING.md
- New screenshot

All the info function names started with "get_", which I removed to make
it easier for the user to configure the program to its needs.
Additionally I renamed some functions (e.g. get_ram_usage) to better
names, making it easier to extend the program with ram usage / total
functions.

Fix some memory leaks

Add diskusage support

add support to show used disk for a given mountpoint

Fixed locale defaulting to English

Changed get_datetime() a bit so it respects the user-configured locale (to use time formats with strings for days, months etc.)

Same commit as last time, except it merges.

minor cleanups and sanity checks