Add per column regex filtering

[erssebaggala]

This PR adds regex filtering for each column. The current version of sqlalchemy-datatables only support regex filtering for the global search.

The regex is used by setting the search_method to regex in the column definition i.e. when creating the ColumnDT instance.

[Pegase745]

Could you add a test please?

[codecov[bot]]

Codecov Report

Merging #108 into master will increase coverage by 0.06%. The diff coverage is 75%.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
+ Coverage   93.68%   93.75%   +0.06%     
==========================================
  Files           1        1              
  Lines         190      192       +2     
==========================================
+ Hits          178      180       +2     
  Misses         12       12

Impacted Files	Coverage Δ
datatables/__init__.py	93.75% <75%> (+0.06%)	:arrow_up:

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[erssebaggala]

@Pegase745 I have added a test for this. The global search regex is failing. The culprit is : https://github.com/Pegase745/sqlalchemy-datatables/blob/d1e686ae400cec1d5899ab9377335b21d88e0e16/datatables/init.py#L350

I could be wrong but from my tests, it is unnecessarily escaping the regex characters.

Why is there a need to clean the regex? Shouldn't it be up to the user to escape any special characters in the search value?

[tdamsma]

I believe the regexes are cleaned for security reasons, as exposing full regex functionality might be a security risk. Not sure how much of a real vulnerability this is with an up to date postgres or mysql backend though.

https://www.owasp.org/index.php/Regular_expression_Denial_of_Service_-_ReDoS https://stackoverflow.com/questions/25269811/is-it-safe-to-let-users-enter-custom-regex-patterns#25269866