Issue 126 - clean up error messages

[lutzhamel]

Cleaned up all error message. For example, the program,

load system io.

let x = 1
io @println "hello".

now issues the message,

Error: msg.ast: 3: term '1' is not a function, did you forget the end-of-line period?

and the program,

function foo with x:%integer do
   return x.
end

foo("hello").

now issues the message,

Error: msg1.ast: 1: actual argument 'hello' not recognized by function 'foo'

[TimColaneri]

Looks great.