ensure all rules operating on constructor function account for ConstructorDeclaration too

[duaraghav8]

#197
duaraghav8/solparse@ff92d99

the new solidity feature constructor() is an alternative way of defining a contract's constructor function. Relevant Rules need to account for this new way that is also acceptable by solparse.

[duaraghav8]

All rules except for those listed in #169 have been modified for this, remaining rules (indentation & lbrace) are huge and complex and in some cases, brittle. Will hopefully fix them too in the near future.