treewide: revise library packaging

- Annotate versionless libraries (such as libubox, libuci etc.) with a fixed
  ABI_VERSION resembling the source date of the last incompatible change
- Annotate packages shipping versioned library objects with ABI_VERSION
- Stop shipping unversioned library symlinks for packages with ABI_VERSION

Ref: https://openwrt.org/docs/guide-developer/package-policies#shared_libraries
Ref: https://github.com/KanjiMonster/maintainer-tools/blob/master/check-abi-versions.pl
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/network/utils/curl/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=curl
 PKG_VERSION:=7.63.0
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://dl.uxnr.de/mirror/curl/ \
@@ -91,6 +91,7 @@ define Package/libcurl
   DEPENDS += +LIBCURL_SSH2:libssh2 +LIBCURL_NGHTTP2:libnghttp2 +ca-bundle
   TITLE:=A client-side URL transfer library
   MENU:=1
+  ABI_VERSION:=4
 endef
 
 define Package/libcurl/config