Add omnisharp--replace-symbol-in-buffer-with
Add omnisharp--current-word-or-empty-string
auto-complete based on the current word

https://github.com/nosami/Omnisharp has a cool list in which order the
completions are ranked:

* CamelCase completions are supported, e.g Console.WL(TAB) will
  complete to Console.WriteLine
* "Subsequence" completions are also supported. e.g. Console.Wline
  would also complete to Console.WriteLine
* Completions are ranked in the following order
    * Exact start match (case sensitive)
    * Exact start match (case insensitive)
    * CamelCase completions
    * Subsequence match completions
Merge branch 'feature-auto-complete-based-on-current-word'