Add .gitignore, remove extra backslash in makefile

Some of the makefile regexes contained one too many backslashes.
On Mac, make/bash (not sure which) seems to ignore the extra backslash,
but on Linux, the extra backslash causes sed to fail to do the proper
replacements.
accidentally broke the pandoc executable path
Merge pull request #1 from ccotter/master

Fix invalid makefile sed commands on Linux