Add support for typographic symbols, like right single quotation mark (’)

[robinmoussu]

Some layout do have direct access to typographic symbols, and user of such layout may prefer to use the typographic version to the ascii version.

• right single quotation mark ’ instead of ' (apostrophe)
• ligatures: œ, æ, … instead of oe, ae, …
• en-dash – instead of the minus sign -

There are other typographic symbols (like „“”«»—, accentuated uppercase letters, non breaking space, …), but I don’t think that they are used in ngram-type.

If possible I think that It would be best to accept either variant indifferently.