Implement simple file io

[daniel-p-gonzalez]

Implement first pass minimal file io.

e.g.

in_file = open('file.txt', 'r')
out_file = open('copy.txt', 'w')

for line in in_file:
  out_file.write(line)
end

Tasks:

• Add wrapper around {i,o}fstream for opening/closing files
• Wrap get_line in for loop iterator for file object
• Auto closing of file handle when leaving scope (*disallow passing file handle to another actor)

• Passing file handles to another actor would be unsafe sharing of state.