Improve logged information when --logfile is provided

[ansasaki]

This adds a better formatter for the logged information when --logfile is provided. It also changes the behaviour of the Single_Logger: a new handler is added every time the Single_Logger factory is called passing a logfile. This may lead to side-effects like doubling the log entries if the same file is passed more than once. Probably it is not the case since the filename is provided only when the new or update command are called.

Fixes #22

[codecov-io]

Codecov Report

Merging #26 into master will increase coverage by 0.47%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #26      +/-   ##
=========================================
+ Coverage   89.42%   89.9%   +0.47%     
=========================================
  Files           2       2              
  Lines         700     703       +3     
  Branches      181     181              
=========================================
+ Hits          626     632       +6     
+ Misses         38      36       -2     
+ Partials       36      35       -1

Impacted Files	Coverage Δ
src/symbol_version/symbol_version.py	89.84% <100%> (+0.47%)	:arrow_up:

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[coveralls]

Pull Request Test Coverage Report for Build 43

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 91.745%

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Totals
Change from base Build 40:	0.3%
Covered Lines:	667
Relevant Lines:	703

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💛 - Coveralls