Filter tweaks

[johnlees]

Changes the default min-count to 5, which works better with a default of strict

Adds the --filter_ambig_as_missing option to align and weed, which alters the min count threshold

Closes #62

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (798c290) 92.65% compared to head (9e55002) 92.50%.

Files	Patch %	Lines
src/cli.rs	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #63      +/-   ##
==========================================
- Coverage   92.65%   92.50%   -0.16%     
==========================================
  Files          16       16              
  Lines        2232     2267      +35     
==========================================
+ Hits         2068     2097      +29     
- Misses        164      170       +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.