Re add in proportion of max count

[timothymillar]

This is very useful for filtering for unique insertions.

[timothymillar]

Added max_count_proportionin in #118 for v0.3.1

Consider adding count proportion metric to every individual sample e.g: sample_2_count_proportion=0.43.

This would allow for quickly filtering to identify unique insertions in a specific sample e.g: tef-filter-gff example.gff.gz --all 'sample_2_count_proportion>=0.9'

[timothymillar]

done in version 0.3.1