🗽New Feature: support pdf format

[rakakroma]

would like to support pdf file but have no idea how to do. any suggestion?

[rakakroma]

This is how Steal the Word works in pdf.js currently....,

While in pdf2htmlEX:

although the latter one need to be transformed by user, it got better display obviously.

The advantage of pdf.js is, it got more chance to get the full sentence by selection (sometimes got the wrong one, though), but pdf2htmlEX divided each sentence into several small blocks, so current method always fail, i am not sure if i can build a custom sentence selection method for it.

Also there's another problem, we got extremely small annotation tooltip in both, that should be fixed.