Added partial BigInt support (#471)

* Added partial BigInt support

Moved from es6 to support bigint

Changed from getNumber to getBigInt

Avoided blobal redeclaration of function/variables

Improved BigInt support, handled bind params for bigInt

Logical change on how big int is supported

BigInt is not fully supported at WASM level

Added config to enable and disable bigInt support

Added documentation

Changed var to const as per readme standard

* Changes as per PR comments

* Changes as per PR comments - future extension support