`assert`s removed from `libtess.cat.js`; new compile target `libtess.debug.js` added

when executing `libtess.cat.js`, `assert` statements were throwing off JS engines wrt inlining, etc. `assert`s are no
w removed from `libtess.cat.js` and a new compilation target, `libtess.debug.js` added which still includes them.
Merge pull request #12 from brendankenny/debugfile

asserts removed from libtess.cat.js; new compile target libtess.debug.js added