corrected wrong word in sentence
added missing underscore in example var-name
Merge pull request #14 from borisdaeppen/minor_typo_fixes

Minor typo fixes
Update chapter1.txt
Typos
Merge pull request #15 from dginev/master

Typos and a brief CFG vs Regular language discussion. Thanks for your contribution, Deyan.
Move chapter3 to chapter4
Update references to chapter4
Move a big part from chapter2 to chapter3
Add links to the next chapter