Quotes as entity references

[MartinPacker]

Single quotes, double quotes, backticks are not available as symbols - using standard HTML entity references. Yes, they can be done using numeric character references.

It's possible Markdown should allow them to be escaped. That's worth considering, too.

[MartinPacker]

• Backtick would be ` or perhaps be backslash escaped. Probably best to support both.
• Double quote would be " or “ or ”, depending. Backslash escaping not a thing.
• Single quote would be ' or ‘ or ’, depending. Backslash escaping not a thing.

[MartinPacker]

Coded all the above and documented. Will be in the next commit and push.

[MartinPacker]

At the same time refactored symbols.py to use a list of tuples. Each tuple is a search term plus its replacement.

[MartinPacker]

Shipped in v4.1