Remove all type specific functions in favor of generic core

[spy16]

• Removes all type check functions from Go code (vector?, string? etc.)
• Adds generic functions like to-type, type and type invocation for initialization
• Adds core.lisp file that defines vector?, string? etc.

[spy16]

I will keep this PR for now. I still need to fix the special forms.. Bit of complexity involved.. Let me know i you have any pointers for the following problem (which unfortunately is also a blocker for macro system):

In some scenarios, an intermediate step is required (in addition to read and eval). For example, when fn* is used to define a function, it needs to walk recursively into the body of the fn* and validate if the forms are correct (For example, (fn* [] (if)) is wrong since if needs more at-lest 2 args, and sabre should throw error when this is executed not when the resultant function is invoked). This works right now, but is very buggy and needs to be re-visited. To understand the current implementation, take a look at analyze function in sabre.

[lthibault]

@spy16 Ok, I'll look into this (probably over the weekend).