Initial directory structure.
fundamental expansion implemented.
undo-friendly delete-and-insert
escape and indent implemented.
elisp eval supported.
refine escape.
field regexp is OK.
Finished constructing the snippet skeleton.
overlay created.
next-field and prev-field implemented. Seems something wrong with the link relationship.
bug about linking of each field group fixed: caused by copy & paste error.
exit-snippet mostly implemented.
bug fix: multiple snippet support
place cursor at a proper position after snippet expanded.
bug fix: wired behavior of synchronize field.
avoid the overlay modification hook to run during snippet creation.
prevent wired behavior of modification hook during undoing
behind-hook implemented
Use cl's defstruct instead of manually maintained poor struct.
Will get to implement yas/overlay in next version.