v0.1.0 feature release

• Implement most important node types given in Parser gem:

Assignments:
lvasgn, ivasgn, cvasgn, gvasgn, op_asgn, or_asgn, and_asgn, masgn, mlhs, casgn

Data types:
nil, true, false, str, xstr, sym, float, regexp, int, hash, pair, array

Key words:
or, and, def, module, yield, break, next, retry, self, rescue, resbody, case, while, until, for, if, return, kwbegin, when

Language elements:
block, args, arg, blockarg, restarg, optarg, kwarg, kwoptarg, kwrestarg, block_pass, splat

Ranges:
irange, erange

Variable types:
const, lvar, ivar, cvar, gvar

Wrappers:
send, begin