Release version 0.3.0

Major changes:
 - Bug when calculating coverage fixed, will affect all results.
 - Concoct can now handle cases where less than 2 contigs were left after length filtering.
 - Calculating coverage for all contigs is now done after per sample normalization.
 - Added Docker as a way of installing Concoct with all its dependencies.
 - Simplifying the SCG analysis by merging three steps into one, using the new COG_table.py script.

Minor changes:
 - More stable colour mapping in the COGPlot.R script. 
 - Addition of execute_complete_example.sh script.