add a function which popup if super key sequences was inputed.

create a value `guide-key/popup-if-super-key-sequence` to make
the new function to be enable/disable.
mod to add the new function.
fix indents to match other codes
bugfix: add guide-key/vbutlast
Merge pull request #2 from kui/master
Rename `guide-key/popup-if-super-key-sequence' to `guide-key/recursive-key-sequence-flag', and modify docstring.
Move TODOs and ChangeLog to README.org.
Change a structure of documentations.
Add a document about `guide-key/recursive-key-sequence-flag'.
Change a name of argument because a function having the same name exists.
Modify typo of README.org.
Bump a version to 1.1.0.