TTFFont.parse should call *Table constructors with explicit @tag param

the bug appears when the library is bundled with browserify+uglify (or any other minify lib); by default uglify task mangle function names so in the `Table` constructor code like `@constructor.name` would return some `'b'`or `'c'`which leads to errors hard to debug (since the problem appears only with the minified versions;  like this one bpampuch/pdfmake#18 or this one bpampuch/pdfmake#60 )

Is it good or bad to rely on function names at runtime (especially if we are targeting the browser)?
See this interesting discussion visionmedia/jade#298 (`uglify` vs `jade`)