mutable string support to lua
$ luarocks install lbuffer
lbuffer is a C module for lua, it provides mutable string feature to
the lua_ language. it has all routines from lua's string module, add
several modify functions. it provides:
* change the value of buffer without copy it.
* a pair of full feature pack/unpack functions.
* get a subbuffer from the original buffer, and the changes to
subbufer will affects the original buffer.