Added inline imports

Now, FL programs can start with any number of import statements. Syntactically,
you can just pretend that import is a function that takes one argument (a
String), and runs all the code at the filename represented by that string
before continuing on to the rest of the code. Currently, import statements must
be at the very beginning, and cannot follow any other statements (except for
other import statements).

Also, ghci takes a filename as its only argument, pointing to the file to read
from, instead of reading from STDIN.