Add function for custom format + tests

[gmuraru]

Fixes #8

Change List:

• add a set_fmt function to the simple and colored logger such to set custom formats for the output log message
• add tests for simple and colored logger for testing the functionality

[gmuraru]

@SebiSebi you still want to offer support for Python2?

[codecov]

Codecov Report

Merging #9 into master will increase coverage by 0.11%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   98.87%   98.98%   +0.11%     
==========================================
  Files           5        5              
  Lines          89       99      +10     
  Branches        5        5              
==========================================
+ Hits           88       98      +10     
  Partials        1        1

Impacted Files	Coverage Δ
friendlylog/colored_logger.py	98% <100%> (+0.22%)	⬆️
friendlylog/simple_logger.py	100% <100%> (ø)	⬆️

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[gmuraru]

Now it should work also for Python 2.7, but maybe it is a good idea to not provide back compatibility anymore since Python2 is dead :(

[mark-bixler]

Wondering if this PR will ever be approved? :)