Addition of gitignore file.

.gitignore

+dist
+cabal-dev
+*.o
+*.hi
+*.chi
+*.chs.h
+.virtualenv
+.hsenv
+.cabal-sandbox/
+cabal.sandbox.config
+cabal.config
+*.aux
+*.log
+*.blg
+*.bbl
+*.DS_Store
+*.synctex.gz
+*.toc
+*.lof
+*.lot
+*.nav
+*.out
+*.snm
+*-nup.pdf