Cobra migration

[hvihvi]

The goal is to have a more extendable octopus toolbox, and a better CLI syntax (the one enforced by cobra).

It should migrate the syntax from git-octopus -args param to octopus merge -args params.

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This change is 

[codecov-io]

Codecov Report

Merging #40 into master will decrease coverage by 0.13%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   94.82%   94.69%   -0.14%     
==========================================
  Files           4        4              
  Lines         174      132      -42     
==========================================
- Hits          165      125      -40     
+ Misses          5        4       -1     
+ Partials        4        3       -1

Impacted Files	Coverage Δ
octopus/git/git.go	100% <ø> (ø)
octopus/merge/matcher.go	100% <ø> (ø)
octopus/merge/config.go	100% <100%> (ø)
octopus/merge/merge.go	90.41% <100%> (ø)

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[hvihvi]

Push --force 0d6d73f : Rebase master and port any new code merged in master to migrated files.