make test position independent
Add benchmarks
compile regexp only once

Go has no regexp cache.

Compiling the regexp only once makes process name normalizations 3x faster
and amortizes on bigger loads and/or lots of threads.

benchmark                       old ns/op    new ns/op    delta
BenchmarkNormlizeProcessName        12539         3566  -71.56%
traverse directories while parsing

Use a goroutine to parse an directory entry while reading the next one.
Not using the path/filepath.Walk to avoid stat calls, sorting and call
overhead.

benchmark                       old ns/op    new ns/op    delta
BenchmarkCollect                  2631962      1747219  -33.62%
Merge pull request #1 from nightlyone/fast_process_iteration

Speed up process metric collection