Displays function signatures from completions in the command line.
Use a package manager and follow its instructions.
Note: echodoc requires v:completed_item feature. It is added in Vim 7.4.774.
The command line is used to display echodoc text. This means that you will
either need to set noshowmode or set cmdheight=2. Otherwise, the -- INSERT -- mode text will overwrite echodoc's text.
When you accept a completion for a function with <c-y>, echodoc will
display the function signature in the command line and highlight the argument
position your cursor is in.