Merge branch 'readme-hotfix'
fix: print error and exit when user expression is empty (issue #103)
fix: print error and exit when user expression is empty or contains only spaces (issue #103)
fix: remove redundant check for invalid user expression (issue #103)
remove test for hawk "" because tested in exprSpec doctest
Merge branch 'issue-103'
Merge branch 'master' of github.com:gelisam/hsl