fix variable shadowing
drop object file size from 20.3 MB -> 1.3 and mapnik.node from 1 MB -> 816 KB
no need for NPROCS variable in Makefile anymore
remove explicit usage of icu::UnicodeString to enable build when -DU_USING_ICU_NAMESPACE=0 is set
gyp cleanups
bump to v1.1.3
fix node engines semver