v is generally used for enabling verbose mode

Compatible with gcc and clang.

Use internal macros for compatibility with non GNUC compilers.

int foo(); declares a function taking any number of arguments.

These feature macros are either define or not defined at all at the
configure step.

Fixes #163

They are nowhere used.

This also fixes an issue with time returned negative if sysconf(_SC_CLK_TCK) returned an error.

The check for NAN is kept to avoid relying on implementation details of the CLAMP macro/function

Fixes #308, thanks @qarmin (Rafał Mikrut)

If currently two unsigned values are compared via `a - b`, in the case b
is actually bigger than a, the result will not be an negative number (as
-1 is expected) but a huge positive number as the subtraction is an
unsigned subtraction.

Avoid over-/underflow affected operations; use comparisons.
Modern compilers will generate sane code, like:
    xor     eax, eax
    cmp     rdi, rsi
    seta    al
    sbb     eax, 0
    ret

It is only used to read process directories on RedHat beginning with a dot.
Unconditionally accept directories with a starting dot.

…sses

Thanks to @adsr for the great work
Closes #241, closes #74
Massive rebase, so #keepfingerscrossed

Shows the process CPU usage divided by the number of CPU cores

- use consistent type for key by introducing a new typedef
- use unsigned types for sizes
- name parameters in foreach function typedef

Dynamically increase the hashmap size to not exceed the load factor and
avoid too long chains.

Switch from Separate Chaining to Robin Hood linear probing to improve
cache locality.

Use primes as size to further avoid collisions.

E.g. on a standard kde system the number of entries in the ProcessTable
might be around 650.

Consistent with everything else involving platform-specific
calls from core htop code.