Merge pull request #4 from hessu/distance

Added missing range.c + .h, missing from pull request for range stats
Don't override CFLAGS. Use cmake commands instead to specify release build
Allow file in /etc/gnuais.conf:

Removed warning message
Added text to README saying that /etc/gnuais.conf overrides user settings
README -> README.md
The text just added to the README was not correct - Corrected
Ignore some common bad coordinates when calculating range