[aucmd] Added automatic window resize when vim window is resized

Change-Id: I455925a9f36096eb6c0ffa3aab149c7e445e8f2d
[aucmd] Added showtabs function

The function unifies and simplifies repeated code regarding showing
tabs in specified filetypes/programming languages

Change-Id: Ib9f8cf0ffc52d0cab30a609bed8cdda866d38359
[doc] Screenshots shifted to rnpvim's wiki

Change-Id: I34ce304881dcbf18089eeeee4d5fb1702adbc956
Merge branch 'cleanup' into next

* cleanup:
  [doc] Screenshots shifted to rnpvim's wiki
  [aucmd] Added showtabs function
  [aucmd] Added automatic window resize when vim window is resized