Few command line options

Basic support for `-n', `-p`, `-a` and `-F` options.

* provides access to filename(s) in `$ARGV`, and current line number (cumulative) in `$.` (this is kludgy, as a variable with this name could not be created.)
* supports only basic strings for split pattern in `-a` and `-F`. When `split` supports regex patterns, this should work.
* `-p` behavior is not identical to Perl, as there is `continue` block to go with `while` loops.
* I am sure there are other limitations that I haven't thought of.