Refactor parseExpr to allow to use the priority precedence

[git-hulk]

This also closes #101

[coveralls]

Pull Request Test Coverage Report for Build 11046163100

Details

• 217 of 285 (76.14%) changed or added relevant lines in 7 files are covered.
• 13 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 59.631%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/ast_visitor.go	6	8	75.0%
parser/parser_table.go	9	12	75.0%
parser/parser_view.go	12	16	75.0%
parser/parser_query.go	24	39	61.54%
parser/parser_column.go	103	123	83.74%
parser/ast.go	58	82	70.73%

Files with Coverage Reduction	New Missed Lines	%
parser/parser_column.go	4	67.25%
parser/ast.go	9	55.76%

Totals
Change from base Build 10935801786:	0.1%
Covered Lines:	6241
Relevant Lines:	10466

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💛 - Coveralls