Implemented: force python 2 or 3 with ability to switch during runtime

Simultaneous python2 and python3 support, switchable during runtime
calling a function as well as setting a variable in .vimrc! Closes
issues #200 and #210 (which gave the idea for this commit, thank you
@Shtucer).

initialize.py

@@ -0,0 +1,25 @@
+''' ------------------------------------------------------------------------
+Python initialization
+---------------------------------------------------------------------------
+here we initialize the jedi stuff '''
+
+import vim
+
+# update the system path, to include the jedi path
+import sys
+import os
+
+# vim.command('echom expand("<sfile>:p:h:h")')
+sys.path.insert(0, os.path.join(vim.eval('expand("<sfile>:p:h:h")'), 'jedi'))
+
+# to display errors correctly
+import traceback
+
+# update the sys path to include the jedi_vim script
+sys.path.insert(1, vim.eval('expand("<sfile>:p:h:h")'))
+try:
+    import jedi_vim
+except ImportError:
+    vim.command('echoerr "Please install Jedi if you want to use jedi_vim."')
+sys.path.pop(1)
+