Implementation of a battery_remaining function which returns the
remaining battery time in HH:MM format. Linux function still needs
implementation.
Move common code to load_apm_power_info

The third value from load_avg (idle) gives us almost the same
information as cpu_iowait. Plus OpenBSD does not offer an iowait value
as Linux and thus the corresponding function would not be portable.

- Battery power cannot be easily gatherable via apm(4)
- IMHO it does not represent essential information

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.