Added CObjError, cosmoV_throw(), pcall(), and cosmoV_printError()

Errors are now handled very differently, parser errors and VM errors are now treated the same.
When cosmoV_error is called, cosmoV_throw is also called, which formats the error object and sets the panic state.
state->error now points to the latest CObjError when state->panic is true. To get a nice formatted Objection message, use
cosmoV_printError() and pass the state->error. pcall() was added to the standard base library. When called, the first argument
passed is called with the subsequent arguments given. If the call completed successfully, `true`,`nil` is returned. However
when an error occurs during the call, `false`,`<error>` is returned. Simply print the `<error>` to retrieve the error string.

src/cosmo.h

@@ -36,6 +36,7 @@ typedef struct CObjUpval CObjUpval;
 typedef struct CObjFunction CObjFunction;
 typedef struct CObjCFunction CObjCFunction;
 typedef struct CObjMethod CObjMethod;
+typedef struct CObjError CObjError;
 typedef struct CObjObject CObjObject;
 typedef struct CObjClosure CObjClosure;