Merge pull request #1 from fy2/fy2-branch

incorporating Feyruz's changes
Rewritten numeric and string operator lessons
Merge branch 'master' of https://github.com/grsr/perl-course

Merging Feyruz's changes with numeric and string lesson changes
fix some typos
Merge branch 'master' of github.com:grsr/perl-course
Condensed array function and hash function lessons into one lesson; moved subroutine lesson up
Rewritten subroutine lesson, made GC content example an exercise
Moved and rewritten references lesson
Merge branch 'master' of github.com:grsr/perl-course
various minor changes
Reordered day 2; minor fixes
rewrote command line argument and sanity check lessons
rewrote file and system call lessons
Update README.md
rewrote the regex lesson
Merge branch 'master' of github.com:grsr/perl-course
add another regex exercise, and mention that split can use regexes
Simplified Lesson 1
Exercises and examples for lessons 1-5
Exercises and examples for lessons 6-9