Allow to add inline parsers to built-in implementation

[zampino]

This is a minimal proposal for allowing the current internal implementation to customize inline parsing of special characters, following @robinst advice to provide a starting POC :-).

I quickly tested this in combination with Parser.Builder.inlineParserFactory in the context of a clojure application for parsing inline latex delimited between pairs of $ characters, but proper testing is still missing. It's a first step to see what's possible, far from providing enough fine-grained customization.

Addresses #263. Closes #317.

[robinst]

So in order for users to actually use this, the configuration needs to be on the Parser.Builder, similar to custom block parsers. Then when constructing the inline parser, pass it in the constructor.

(We will also need to move some classes into an exported package, but can do that later.)

[robinst]

So this will currently override any existing built-in parsers with that same special character. I think we should do the same thing as for block parsers, see

commonmark-java/commonmark/src/main/java/org/commonmark/parser/Parser.java

Line 208 in 1bf85c6

public Builder customBlockParserFactory(BlockParserFactory blockParserFactory) {

So try the custom parsers first. The custom parser can decide not to handle something, in which case the built-in parsers are tried next.

[robinst]

Closing this in favor of

• Support for extending inline parsing with custom inline content parsers #321