Update documentation for 3.x.

[artem-zinnatullin]

Most of documentation is actually compatible with 3.x, but specifically section about downloading and keeping Mainframer will need to be updated as we switch to distribution through Homebrew and other package managers #32 and OS-wide usage #185.

[arturdryomov]

I have a radical proposition to streamline things and remove the baggage.

The proposed documentation structure:

.
└── docs
    ├── configuration
    │   ├── mainframe.md
    │   ├── user-examples.md
    │   └── user.md
    ├── integrations
    │   └── intellij-idea.md
    └── setup
        ├── mainframe.md
        └── user.md

• As you can see I’ve replaced local and remote terms with user (as user terminal) and mainframe. Over time I feel that everybody invents their own name for machines and we might as well bring our own terms more in line with the Mainframer naming. Hopefully it will stick better.
• Recipes are gone since the naming was wrong all along. In my understanding recipes are more about how to use the tool instead of how to use other tools with the tool.
• Samples are gone for a couple of reasons: it is painful to support them, as tests they play zero to none purpose (otherwise the test suite is bad) and, more importantly, GitHub traffic stats show that people do not open them (except the Android one but we have Android Studio docs here for some reason). I’ve replaced them withconfiguration/user-examples.md which will contain various ignore.yml which actually play a purpose in samples.
• Not to worry — configuration/mainframe.md will contain a single phrase like _Mainframe does not have any configuration except SSH`.

@artem-zinnatullin, if you agree, I can start implementing this.

[artem-zinnatullin]

In general I'm in favor of change, but I do have comments

• Definitely not a fan of "mainframe" and "user" (wut), I'd like us to be consistent with configs and use same terminology, like "remote" and "local"
• "user-examples" should be a directory similar to "integrations", imo, it looks weird in "configuration" dir

[arturdryomov]

Thought about configs as well but we use push and pull already.

[artem-zinnatullin]

Damn it

[artem-zinnatullin]

Wait, we still have "remote" in config, let's keep "remote" and "local" then?