eodoc: generator of HTML documentation from EO sources

[yegor256]

We need to create a documentation generator. It has to be called as eoc doc. It should execute register and parse beforehand, and then simply scan all available .xml files take object documentation from it, for example:

# This is the documentation, explaining how to use
# this object:
#
# ```
# this is fixed-font
# Markdown block
# ```
#
# Markdown can be here [too](some-link)
[x] > foo
  Q.io.stdout > @
    "Hello, world!\n"

Here, the entire block above the object will be in the XML produced by the parser. We should create xxx.html for each xxx.xml file. It would be great to use XSL for this generator. Also, we should create HTML files for each package, similar to how JavaDoc does it.