windows support

[mcuadros]

based on appveyor, many tests are falling, will be good fix this issues:
https://ci.appveyor.com/project/mcuadros/go-git

[mcarmonaa]

PRs to solve it:

• *: windows support, some more fixes #533
• *: windows support, some more fixes (2) #536

About those failed tests with this kind of messages, they aren't solved (idk how to solve them):

*net.OpError = &net.OpError{Op:"read", Net:"tcp", Source:(*net.TCPAddr)(0xc042009e00), Addr:(*net.TCPAddr)(0xc042009e30), Err:(*os.SyscallError)(0xc0424559c0)} ("read tcp [::1]:1084->[::1]:1082: wsarecv: An existing connection was forcibly closed by the remote host.")

*net.OpError = &net.OpError{Op:"write", Net:"tcp", Source:(*net.TCPAddr)(0xc042008660), Addr:(*net.TCPAddr)(0xc042008690), Err:(*os.SyscallError)(0xc042264100)} ("write tcp [::1]:1088->[::1]:1087: wsasend: An existing connection was forcibly closed by the remote host.")

They aren't related to IPs (v4/v6). It seems that git for windows has issues with git:// protocol as it said here. I tried to set the workaround mentioned in the issue for each repository used in the tests but the fails kept there.

Other reason for the fails could be the configuration app veyor uses for its VM.

[mcuadros]

For the git protocol tests, for windows the read-only operations can be tested against GitHub.

[mcarmonaa]

@mcuadros read-only operations are already being tested against GH. They are ok, don't fail.

About write-operations tests, should they be just skipped in case of windows to avoid fails for the moment?

[mcuadros]

Yaup

[mcarmonaa]

Done in #540