Add new options to Autolink

[keitaf]

This will add the following options to Autolink.

• symbolTag: a tag to apply around symbol (#,@,$) in hashtag/username/list/cashtag links.
• textWithSymbolTag: a tag to apply around text part in hashtag/username/list/cashtag links.
• urlTarget: the value of target attribute in URL links
• linkAttributeModifier: modifies attributes of a link based on the entity.
• linkTextModifier: modifies text of a link based on the entity.

Examples:

  linker.setSymbolTag("s"); linker.autoLink("#hash") => "<a...><s>#</s>hash</a>"

  linker.setTextWithSymbolTag("b"); linker.autoLink("#hash") => "<a...>#<b>hash</b></a>"

  linker.setLinkAttributeModifier(new LinkAttributeModifier() {
    @Override public void modify(Entity entity, Map<String, String> attributes) {
      if (entity.type == Type.HASHTAG) attributes.put("custom-attr", "some_value");
     });
  linker.autoLink("#hash") => "<a.. custom-attr="some_value"...>#hash</a>"
  linker.setLinkTextModifier(new LinkTextModifier() {
    @Override public CharSequence modify(Entity entity, CharSequence text) {
      return entity.type == Type.HASHTAG ? "prefix"+text : text;
     });
  autoLink("#hash") => "<a...>prefix#text</a>"

This will also change urlClass option, which is currently applied to all links but will only be applied to URL links.