Basic server mode support

[st0012]

Currently, rdoc doesn't support server mode, which makes both using it and developing it extremely inconvenient.

(ri --server is RI's web interface, which lets users read indexed RI documents in the browser. It does NOT run current project's RDoc documentation in server mode. To avoid confusion, I moved RDoc::Servlet to RDoc::RI::Servlet.)

So in this PR, I want to introduce a very rough server support to RDoc:

• Can be used with rdoc --server or rdoc -s
  • It's marked as experimental for now as it's very slow (see below)
  • The port defaults to 4000 but can be assigned with --port=PORT
• Will use a tmpdir to temporarily host the generated files so they don't override the original doc folder
• It reparses and regenerates files on EVERY SINGLE REQUEST, which is pretty slow, but still faster than running rdoc or rake rdoc repeatedly
  • We can add smarter reparsing/regenerating support, but it will first take some refactoring as the current design doesn't account for those

[faustind]

Hi @st0012

Please tell me: Will your work here allow one to consult the standard library's documentation locally using rdoc?

ri's server mode seems to require the installation of webrick. Will rdoc --server have the same dependency?

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edit

Never mind 😅 I saw the requirement on webrick in the Gemfile. And ri's server mode already allows consulting the Ruby docs locally 👍🏾