Updated the link to Antlr in README

When following the link to Antlr in the README while browsing the repository on GitHub, if the Url isn't designated as an external link it tries navigating to the a file in the local repository.
Merge pull request #21 from kopelli/patch-1

Updated the link to Antlr in README
Updated authorship/copyright statements.
Calculator: add negative numbers, modulo and power operator and Math functions
Report useful error message when function cannot be found
Merge pull request #23 from tibel/master

LinqyCalculator: additonal operators and math functions