runtime: load rum file

[avelino]

ref: https://github.com/rumlang/rum/issues/60#issuecomment-350722270

load: load file .rum this file point

test1.rum

(print "print test1")

main.rum

(package "main"
  (print "start")
  (load "test1.rum")
  (print "end"))

output:

start
print test1
end

load differs from import, import as object where it is possible to use as Object: ex (import test2) (print test2.Function)

Multi load (load "test1.rum" "test2.rum")