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)

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.

add support to show used disk for a given mountpoint

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.

add a short sleep to reduce load

The buffer being hardcoded to 19 (the size expected from the default time format),
strftime() would fail on any format returning a longer buffer.
Changed it from 19 to 64 to accomodate longer formats.

Former : MemTotal - MemAvailable
New : (MemTotal - MemFree) - (Buffers + Cached)

Fixed indentation
Removed trailig white spaces