Improve/format the README and docs

Support `fzf#run()`’s `exit` option in `fzf_tjump#jump()`

Adjust cursor position after jump

Use `executable()` instead of `filereadable()`

Support `g:loaded_fzf_tjump` to disable the plugin

Fix demo

Use `.mp4` demo

Refer the documentation

Fix cases: use "CR" instead of "Cr"

Fix whitespaces

Use "z" named register to get selected text

Fix a mapping: use `xnoremap` for Visual mode

Add an option `g:fzf_tjump_preview_options` for fzf's `--preview-window`

Update tagstack before jump

Fix indentations