Add `index` command and change default install dir for `install` command

[CD3]

I've implemented an index command for managing local conan recipe indexes. This makes it easy to add conan remotes from git repositories.

For example:

$ cppship index add --name cd3 --git https://github.com/CD3/cd3-conan-packages

This will clone the git repository to ~/.cppship/index_store/cd3 and add that directory as a local package index so you can use the recipes in the index as conan dependencies.

I also updated the install command. It started as a fix to create the destination directory and all parents so you don't get an error if you try to install to a directory that does not exist, and then I added a --root option and changed to default install location to ~/.cppship/bin to reflect cargo.

[qqiangwu]

Awesome.

Can you please split the pr into two, one for install command and one for index command so that I can review it easier?

[qqiangwu]

In addition, remove the publish command for the moment.

[CD3]

Yes, I was going to do that but ran out of time this morning. I'll split it into the install command update and the index command addition on top of that (it depends on the function added to support the install update).

I removed the publish command from main but forgot to clean up the other files.

Probably won't be able to do anything for a few day.