Add a way to profile Vim bindings

docs/source/develop/tips-and-tricks.rst

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+****************************************
+Tips and tricks for powerline developers
+****************************************
+
+Profiling powerline in Vim
+==========================
+
+Given that current directory is the root of the powerline repository the 
+following command may be used:
+
+.. code-block:: sh
+
+    vim --cmd 'let g:powerline_pyeval="powerline#debug#profile_pyeval"' \
+        --cmd 'set rtp=powerline/bindings/vim' \
+        -c 'runtime! plugin/powerline.vim' \
+        {other arguments if needed}
+
+After some time run ``:WriteProfiling {filename}`` Vim command. Currently this 
+only works with recent Vim and python-2*. It should be easy to modify 
+:file:`powerline/bindings/vim/autoload/powerline/debug.vim` to suit other 
+needs.

powerline/bindings/vim/autoload/powerline/debug.vim

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+python import cProfile
+python powerline_pr = cProfile.Profile()
+
+function powerline#debug#profile_pyeval(s)
+	python powerline_pr.enable()
+	try
+		let ret = pyeval(a:s)
+	finally
+		python powerline_pr.disable()
+	endtry
+	return ret
+endfunction
+
+function powerline#debug#write_profile(fname)
+	python import vim
+	python powerline_pr.dump_stats(vim.eval('a:fname'))
+	python powerline_pr = cProfile.Profile()
+endfunction
+
+command -nargs=1 -complete=file WriteProfiling :call powerline#debug#write_profile(<q-args>)