Replace curly quotes by regular quotes for searching

Fixes #1399.

Note that this fixes searching not only for the document referenced in the issue, but also for many other documents that I have encountered on the internet. Lots of documents use curly quotes, but almost no one uses those when searching.
Move the normalization into separate function, please also include other symbols such as angle quotes and probably 'tm', 'R', '1/2' etc. You might what to apply that once. But I would recommend to search only for letters and digits and discard the punctuation (and sometimes spaces)