feat: add filtering of input data

[pohlt]

Some package data contains Unicode characters which
might cause problems for certain output formats (in
particular ReST tables). This commit adds filtering
functionality by introducing two new options.

[codecov]

Codecov Report

Merging #76 into master will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
+ Coverage   98.45%   98.52%   +0.06%     
==========================================
  Files           1        1              
  Lines         323      338      +15     
==========================================
+ Hits          318      333      +15     
  Misses          5        5              

Impacted Files	Coverage Δ
piplicenses.py	98.52% <100.00%> (+0.06%)	⬆️

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[raimon49]

@pohlt Thanks!!

I've confirmed that your implementation of --filter-strings provides great behavior. 👍

$ pip-licenses -d --format=rest
+------+---------+---------+-----------------------------------------+
| Name | Version | License | Description                             |
+------+---------+---------+-----------------------------------------+
| poyo | 0.5.0   | MIT     | A lightweight YAML Parser for Python. 🐓 |
+------+---------+---------+-----------------------------------------+

$ pip-licenses -d --format=rest --filter-strings
+------+---------+---------+----------------------------------------+
| Name | Version | License | Description                            |
+------+---------+---------+----------------------------------------+
| poyo | 0.5.0   | MIT     | A lightweight YAML Parser for Python.  |
+------+---------+---------+----------------------------------------+

After merging this P-R I plan on shipping the next version 2.3.0.