Adds external protocol insertion for the clients and protocol selection based on the scheme

[alcortesm]

This patch allows the user to inject its own protocols to access git repositories, not just the standard HTTP and SSH.

It also adds automatic selection of the protocol to use based on the scheme of the URL of the repository.

[codecov-io]

Current coverage is 68.24%

Merging #10 into master will decrease coverage by -0.15% as of f0b4516

@@            master     #10   diff @@
======================================
  Files           17      17       
  Stmts         1199    1203     +4
  Branches       191     191       
  Methods          0       0       
======================================
+ Hit            820     821     +1
- Partial         92      93     +1
- Missed         287     289     +2

Review entire Coverage Diff as of f0b4516

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[toqueteos]

LGTM