WIP: v2 impl

[caarlos0]

refs #128

This is a full rewrite of the core APIs, now we have:

• better error handling
• ability to easily add support to other kinds of stuff, like fish plugins, for instance. I already added Path support (add the bundle to the path instead of look for files) to prove the concept, and all is working
• the code is probably better organized with the division of the Project and Bundle concept: Project is a git, local, bzr or whatever project, downloaded or not. Bundle encapsulates a project and can resolve how to use it (example: Path, Zsh, Fish)
• --static is now the default (the only broker api change). Basically, everything passed down to bundle will return a source path or export PATH=blah or whatever the Project impl does

Whats missing:

• check possible bug when dealing with url->folder->url maps. Possible buggy in stable too
  • probably better to put this URL-dealing stuff in a separated package
• check if there are any todos left and do them
• update readme
• battle test everything again
• release!

This will be v2.0.0. Actual v0.9.x will be promoted to v1.0.0 and for now on will receive only bugfixes

[mention-bot]

@caarlos0, thanks for your PR! By analyzing the annotation information on this pull request, we identified @twang-rs to be a potential reviewer

[houndci-bot]

exported function NewLocal should have comment or be unexported

[houndci-bot]

exported function Shell should have comment or be unexported

[coveralls]

Coverage remained the same at 100.0% when pulling 94fc3af on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 94fc3af on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling f6890ec on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling ada47e2 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 46eff91 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 6582630 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 3a1e466 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 80cb5c9 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling fe755c6 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 918e96d on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling ff82bd2 on next into 973a8a8 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 151ede9 on next into 973a8a8 on master.