Disallow numeric constant name

[tangrufus]

close #4

Note: There are a few more constant names will break, e.g: null, true, false.
Haven't think of a good way to catch them all.

[coveralls]

Pull Request Test Coverage Report for Build 39

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 38:	0.0%
Covered Lines:	19
Relevant Lines:	19

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💛 - Coveralls

[QWp6t]

Update: I just noticed that you mentioned this in #4 and the intention of this PR is to disable that behavior anyway.

Fair enough. 😅

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It's technically valid to use numeric constants. You can access them using the constant() function.

null, true, and false are already predefined constants, so they should already fail if a user attempts to redefine them.