Reorganization of solgo path structure

[0x19]

Does not make sense that all of the go code is in the main path. Instead, I've built sub packages for now for contracts and abis. As well introduced common.

Abis is intentional as a lot of packages in go use "abi" package name so making it "abis" creates imports easier.

[coveralls]

Pull Request Test Coverage Report for Build 5436941273

• 33 of 40 (82.5%) changed or added relevant lines in 4 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+2.7%) to 68.387%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
abis/parser.go	27	34	79.41%

Files with Coverage Reduction	New Missed Lines	%
solgo.go	2	94.29%

Totals
Change from base Build 5431386318:	2.7%
Covered Lines:	424
Relevant Lines:	620

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💛 - Coveralls