docs/installation: clarify and reorder alternative installation methods - Add an introduction describing the different installation methods and their pros/cons. - Clarify that Python 3.x is not currently supported. - Move standard pip install method as last method, and rename as also in virtualenv we are installing from Python Package Index.

syntax: glob
*.pyc
*.swp
*.sqlite
*.tox
*.egg-info
*.egg

syntax: regexp
^rcextensions
^build
^dist/
^docs/build/
^docs/_build/
^data$
^sql_dumps/
^\.settings$
^\.project$
^\.pydevproject$
^\.coverage$
^kallithea\.db$
^test\.db$
^Kallithea\.egg-info$
^my\.ini$
^fabfile.py
^\.idea$