- 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

add a short sleep to reduce load

Fixed small buffer in get_datetime()

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.