Python JSONPath Version 2

[jg-rp]

Looking ahead to Python JSONPath version 2, this PR includes breaking changes for both the Python API and some subtle changes to the default JSONPath syntax. We have:

• Changed the lexer so it emits more punctuation and whitespace tokens. Previously we broadly skipped some punctuation and whitespace. Now the parser can make better choices about when to accept whitespace and do a better job of enforcing dots.
• Rewritten the parser and its token stream. It should now be more correct and easier to read.
• Changed the internal representation of JSONPath segments and selectors. We now model segments explicitly.
• Renamed "fake root" to "pseudo-root"
• Dropped support for unquoted property names in bracketed segments.

More changes to follow before release:

• Implement the Singular path selector.
• Implement the keys filter selector.
• Remove shorthand arguments to some selector classes. We no longer need them.
• Improve leading and trailing whitespace handling options so users can choose how strict to be.

[jg-rp]

Some JSONPath performance notes, before attempting any new optimizations.

This benchmark is run on lots of small JSONPath queries with small data.

Main branch (89c0e7e)

(python-jsonpath) james@Jamess-Mac-mini python-jsonpath % python scripts/benchmark.py 
repeating 436 queries 100 times, best of 3 rounds
compile and find               1.392
compile and find (values)      1.400
just compile                   0.917
just find                      0.392
just find (values)             0.395

V2 branch (e41ec29)

(python-jsonpath) james@Jamess-Mac-mini python-jsonpath % python scripts/benchmark.py
repeating 436 queries 100 times, best of 3 rounds
compile and find               1.461
compile and find (values)      1.471
just compile                   0.949
just find                      0.413
just find (values)             0.418