Add cache-control header and config entry to manage it, closes Crunch…

…yData#71

Add an example of using a non-Mercator projection

fix ci script

Merge branch 'master' of github.com:CrunchyData/pg_tileserv

Merge pull request CrunchyData#26 from kbatuigas/doc2

Forgot the deletes

put usage before examples

add tagged builds