Preview/action not working with `fzf-find-in-buffer`

[Cibin Mathew]

Feature request
fzf-find-in-buffer was added in #96 and preview support was added later for few methods in #102

It would be great to have

1. preview available for fzf-find-in-buffer as well.
   note: fzf-find-in-buffer candidates contain only line number and text (no filepath since it is current buffer)

2. action that takes to the line location on choosing a candidate

[Kenshin]

I try twice to add a preview, but failed. It's really vary hard to add preview feature. Instead, you can use "goto-line-preview" plugin. but it only accept a line number as input.