refactor code. Expose new API to add/remove markers
add marker reach callback, with marker object as callback argument
Allow higher flexibity for marker/overlay text. Now it is registered as a callback function which return the display string
add 'destroy' and 'reset' method. Also the player API can only be obtained through player function to avoid users keeping a reference to it
add grunt to compile/minify source files
fix styling bug with less
fix a bug in removing markers
fix a bug for registering markertip evernts when it is disabled
remove get api function
allow adding marker classes
rename display time
update display_time to displayTime for consistency
update README
recompile source files
update example
fix styling bug of break overlay
compile
update
fix bug with sorting markers array