refactor: LexParse API

[ianlewis]

Description:

Refactors the lexparse API.

lexparse

• LexParse now accepts a Lexer and Parser as parameters instead of the initial states. Both the lexer and parser are run in their own goroutines.

lexer

• Renames State to LexState
• Renames StateFn to LexStateFn
• Lexer no longer creates a goroutine. Callers are now responsible for any necessary goroutines.
• Callers now pass a chan *Lexeme to NewLexer and NewParser allowing the caller more control over the lexeme channel.

parser

• Adds a new ParseState type to represent parser state.
• Adds a new ParseStateFn to easily convert a state function into a ParseState.
• Parser internal state is now protected by a sync.Mutex
• Removed Node.Left, Node.SetLeft, Node.Right, Node.SetRight, Parser.RotateLeft, Parser.RotateRight.

Related Issues:

Fixes #69

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.79310% with 9 lines in your changes missing coverage. Please review.

Project coverage is 89.54%. Comparing base (ec3a3dd) to head (70a101c).

Files with missing lines	Patch %	Lines
parser.go	91.89%	5 Missing and 1 partial ⚠️
lexer.go	93.75%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #88      +/-   ##
==========================================
- Coverage   91.48%   89.54%   -1.95%     
==========================================
  Files           3        3              
  Lines         470      373      -97     
==========================================
- Hits          430      334      -96     
+ Misses         30       28       -2     
- Partials       10       11       +1     

Files with missing lines	Coverage Δ
lexparse.go	100.00% <100.00%> (ø)
lexer.go	86.87% <93.75%> (+0.40%)	⬆️
parser.go	91.93% <91.89%> (-4.65%)	⬇️