feat: cycle previewers with commit and bcommit already using it (#528)

- new git previewers
- jump to line in bcommit previewer
- vimdiff for bcommits
- dynamic preview window titles
- more previewers documentation

Cycle previewers are not mapped yet. So you need to setup yourself:
```lua
require('telescope').setup {
  defaults = {
    mappings = {
      i = {
        ["<C-s>"] = actions.cycle_previewers_next,
        ["<C-a>"] = actions.cycle_previewers_prev,
      },
    },
  }
}
```

Co-authored-by: Thore Strassburg <thore@weilbier.net>

lua/telescope/make_entry.lua

@@ -248,8 +248,7 @@ function make_entry.gen_from_git_stash()
   end
 end
 
-
-function make_entry.gen_from_git_commits()
+function make_entry.gen_from_git_commits(opts)
   local displayer = entry_display.create {
     separator = " ",
     items = {
@@ -281,7 +280,8 @@ function make_entry.gen_from_git_commits()
       value = sha,
       ordinal = sha .. ' ' .. msg,
       msg = msg,
-      display = make_display
+      display = make_display,
+      current_file = opts.current_file
     }
   end
 end