Remove carriage return characters in version file

Fixes #566

When created on Windows, .rbenv-version or .ruby-version files may have CR characters that will prevent rbenv from correctly parsing the Ruby version. Discard those characters when reading the file.

Updated README.md; Commands moved to COMMANDS.md.

Also added `help` output for `pyenv {,un}install`, since those sections didn’t exist before.

They should probably be revised at some point.  In the meantime, I think something is better than nothing (in this case).

README.md: Minor edits and formatting

fix: anaconda_architecture mispelled MacOSX as MaxOSX

Add CPython 3.4.0

This prevents the tests from removing an existing directory.

Fixes #561 (https://github.com/sstephenson/rbenv/issues/561)

This greatly improves the performance of `pyenv virtualenvwrapper_lazy`,
which happens to call pyenv-which a lot.

For profiling I've initially used:

    % zmodload zsh/zprof
    % eval "$(pyenv init -)"
    % pyenv virtualenvwrapper_lazy

    Before:
    % zprof|grep -E '(pyenv|virtualenv)'
     1)    1         754,07   754,07   58,95%    751,50   751,50   58,75%  pyenv
    21)    1           2,57     2,57    0,20%      2,57     2,57    0,20%  virtualenvwrapper_setup_lazy_loader
     1)    1         754,07   754,07   58,95%    751,50   751,50   58,75%  pyenv
           1/1         2,57     2,57    0,20%      2,57     2,57             virtualenvwrapper_setup_lazy_loader [21]
           1/1         2,57     2,57    0,20%      2,57     2,57             pyenv [1]
    21)    1           2,57     2,57    0,20%      2,57     2,57    0,20%  virtualenvwrapper_setup_lazy_loader

    After:
    % zprof|grep -E '(pyenv|virtualenv)'
     1)    1         383,30   383,30   27,97%    380,88   380,88   27,79%  pyenv
    31)    1           2,42     2,42    0,18%      2,42     2,42    0,18%  virtualenvwrapper_setup_lazy_loader
     1)    1         383,30   383,30   27,97%    380,88   380,88   27,79%  pyenv
           1/1         2,42     2,42    0,18%      2,42     2,42             virtualenvwrapper_setup_lazy_loader [31]
           1/1         2,42     2,42    0,18%      2,42     2,42             pyenv [1]
    31)    1           2,42     2,42    0,18%      2,42     2,42    0,18%  virtualenvwrapper_setup_lazy_loader

Fixes https://github.com/yyuu/pyenv-virtualenvwrapper/issues/13

Addendum for `pyenv install` usage

This gives users an idea of which versions of python are available. Other version managers ([nvm](https://github.com/creationix/nvm), [rvm](https://rvm.io/rubies/list), etc) tell users how to list available versions as well.

Added python 3.3.5rc2

Added python 3.3.5rc1 and 3.4.0rc2