Support "undocumented" features (AND, XOR, etc)

[simonpoole]

AND, XOR and other stuff as listed here https://github.com/simonpoole/JosmFilterDoc/pull/1 that could only be found by reading the code, thanks to @Woazboat for taking the time to dissect the JOSM code.

• [x] AND
• [x] XOR
• [x] key?
• [x] key:
• [ ] backslash escape in literals and quoted strings. This can't be reasonably added in literals, \" and \ are supported in quoted strings.

Naturally a bit of head banging is required to grasp how you can have undocumented reserved terms in any kind of grammar.

[simonpoole]

AND is already supported

[simonpoole]

XOR in https://github.com/simonpoole/JosmFilterParser/commit/ef67735e84fe32078650cb69a2027b03af648d8e

[simonpoole]

Exact key match in https://github.com/simonpoole/JosmFilterParser/commit/612e9566068d9e34ef264dbb1b3c5be3f90639b3

[simonpoole]

Boolean value matching added in https://github.com/simonpoole/JosmFilterParser/commit/69809cf1cb2e0e34ce7a0a330d1554049ccc6834