Add support for python virtualenv (#12)

* Add support for python virtualenv

* Fix missing $ when using virtualenv color variables

* Add Python Virtualenv section to the TOC

* Add an env variable to control the python virtualenv surrounding parens color

* Avoid an extra white space on the rprompt when the virtualenv is empty

README.md

@@ -36,6 +36,7 @@ For a fish compatible version of this theme have a look at [slimfish](https://gi
     - [User and Host Info](#user-and-host-info)
     - [AWS Profile Info](#aws-profile-info)
     - [Auto Correction](#auto-correction)
+    - [Python Virtualenv](#python-virtualenv)
     - [Git Information](#git-information)
         - [Gitline](#gitline)
 - [Example](#example)
@@ -183,6 +184,20 @@ Defines the color of the misspelled string for which is correction is proposed.
 
 Defines the color of the proposed correction of a misspelled string. Default is `green`.
 
+### Python Virtualenv
+
+##### `SLIMLINE_DISPLAY_VIRTUALENV`
+
+Defines whether active python virtualenv shall be displayed. Default is `1`.
+
+##### `SLIMLINE_VIRTUALENV_COLOR`
+
+Defines the color of the virtualenv name. Default is `cyan`.
+
+##### `SLIMLINE_VIRTUALENV_PARENS_COLOR`
+
+Defines the color of the parens surrounding the virtualenv name. Default is `white`.
+
 ### Git Information
 
 ##### `SLIMLINE_ENABLE_GIT`

slimline.zsh

@@ -74,6 +74,12 @@ prompt_slimline_cwd() {
   echo "%F{${cwd_color}}%3~%f "
 }
 
+prompt_slimline_virtualenv() {
+  local parens_color="${SLIMLINE_VIRTUALENV_PARENS_COLOR:-white}"
+  local virtualenv_color="${SLIMLINE_VIRTUALENV_COLOR:-cyan}"
+  [ $VIRTUAL_ENV ] && echo "%F{$parens_color}(%f%F{$virtualenv_color}`basename $VIRTUAL_ENV`%f%F{$parens_color})%f"
+}
+
 prompt_slimline_set_prompt() {
   local symbol_color=${1:-${SLIMLINE_PROMPT_SYMBOL_COLOR_WORKING:-red}}
 
@@ -106,6 +112,14 @@ prompt_slimline_set_rprompt() {
   if [[ -n "${_prompt_slimline_git_output:-}" ]]; then
     RPROMPT+="${RPROMPT:+ }${_prompt_slimline_git_output}"
   fi
+
+  # add virtualenv (if active and not empty)
+  if (( ${SLIMLINE_DISPLAY_VIRTUALENV:-1} )); then
+    local virtual_env="$(prompt_slimline_virtualenv)"
+    if [[ -n "${virtual_env}" ]]; then
+      RPROMPT+="${RPROMPT:+ }${virtual_env}"
+    fi
+  fi
 }
 
 prompt_slimline_set_sprompt() {