Add --lib-only configure option
Add --lib-only configure option

This is a short hand for --disable-app --disable-examples
--disable-hpack-tools --disable-python-bindings, for users who want to
build libnghttp2 only.

icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2,icing/nghttp2