Added segment for python-venv. Includes feature/npm-segment changes

[Enprogames]

Sorry about the messy commit.

This allows for a python virtual environment to be displayed at the beginning of the powerline. This is basically achieved by calling the $VIRTUAL_ENV variable and seeing if it has a value. If it does, the venv_info variable is set to 'venv'. It then looks for a venv/pyvenv.cfg file, which is how the python-venv package stores its configuration. If this file has a prompt variable, it uses this as the prompt at the beginning of the powerline. This can be seen in the image below:

This is done with the following code on line 87:

function __powerline_python_virtual_env_prompt {
  local venv_path="$VIRTUAL_ENV"
  local color=${VIRTUAL_ENV_PROMPT_COLOR}
  local venv_info=""
  if [[ "$venv_path" != "" ]]; then

    if [[ -f "venv/pyvenv.cfg" ]]; then 
      shopt -s extglob
      configfile="venv/pyvenv.cfg" # set the actual path name of your (DOS or Unix) config file
      while IFS=' =' read -r lhs rhs
      do
          if [[ ! $lhs =~ ^\ *# && -n $lhs ]]; then
              rhs="${rhs%%\#*}"    # Del in line right comments
              rhs="${rhs%%*( )}"   # Del trailing spaces
              rhs="${rhs%\"*}"     # Del opening string quotes 
              rhs="${rhs#\"*}"     # Del closing string quotes 
              if [[ ! $lhs == *-* ]]; then
                declare $lhs="$rhs"
              fi
          fi
      done < $configfile
      eval prompt=$prompt
      venv_info="$prompt"
    else
      venv_info=$(basename ${venv_path})
    fi
  fi
  [[ -n "${venv_info}" ]] && echo "${venv_info}|${color}"
}