pango rbpangoattributes.c: drop PANGO_CHECK_VERSION < 1.14
pango rbpangofontface.c: drop PANGO_CHECK_VERSION < 1.14
pango rbpangofontfamily.c: drop PANGO_CHECK_VERSION < 1.14
pango rbpangofontmap.c: drop PANGO_CHECK_VERSION < 1.14
pango rbpango.h: drop PANGO_CHECK_VERSION < 1.14
add required libpango version
update READMEs