feat: Initial support for DECLARE (cursors)

[ovr]

Hello!

It requires support for arguments, but it's a good initial point for supporting DECLARE.

Thanks

[coveralls]

Pull Request Test Coverage Report for Build 2446379753

• 56 of 59 (94.92%) changed or added relevant lines in 3 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 89.772%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/parser.rs	24	25	96.0%
src/ast/mod.rs	23	25	92.0%

Files with Coverage Reduction	New Missed Lines	%
src/ast/mod.rs	1	78.76%

Totals
Change from base Build 2440505971:	0.03%
Covered Lines:	8698
Relevant Lines:	9689

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💛 - Coveralls

[alamb]

Thanks @ovr

[alamb]

@ovr thank you -- For some reason github says this PR has a conflict -- can you possibly do so and I'll merge it in?

Thanks again!

[ovr]

@alamb Rebased ✅

[alamb]

Looks great -- thanks again @ovr