Small documentation update
Improved QIIME file detection by FormatGuesser

QIIME files do not need to have a header line containing 'QIIME'
More tests for QIIME format detection
More (failing) tests for GAAS

Tests do not pass yet. Need to fix.
Skip to end if no more formats left to try
Tightened QIIME and GAAS format detection
More QIIME format tightening
Slight modification of GAAS test files
Better format detection by identifying numerical columns
Regexp to match number must be anchored
Removed code to check previous line

It was adding assumptions and is now obsolete due to the checks on numerical columns introduced in the few previous commits
Code optimizations