common/: add support for changelog field.

This commits allows ./xbps-src show to show the changelog field and for
changelog to be included with the -c/--changelog option via xbps-create.

Closes: #14102 [via git-merge-pr]

Manual.md

@@ -579,6 +579,9 @@ Example:
 A list is composed of three components separated by a colon: group, symlink and target.
 i.e `alternatives="vi:/usr/bin/vi:/usr/bin/nvi ex:/usr/bin/ex:/usr/bin/nvi-ex"`.
 
+- `changelog` URL to the changelog of the package, the changelog must be in plaintext.
+i.e `changelog="https://raw.githubusercontent.com/user/package/master/CHANGELOG.md"`
+
 <a id="explain_depends"></a>
 #### About the many types of `depends` variable.
 

common/environment/setup/sourcepkg.sh

@@ -2,7 +2,7 @@
 # the package template (excluding subpackages).
 
 ## VARIABLES
-unset -v pkgname version revision short_desc homepage license maintainer
+unset -v pkgname version revision short_desc homepage changelog license maintainer
 unset -v only_for_archs distfiles checksum build_style nocross broken
 unset -v configure_script configure_args wrksrc build_wrksrc create_wrksrc
 unset -v make_build_args make_check_args make_install_args

common/hooks/do-pkg/00-gen-pkg.sh

@@ -74,6 +74,7 @@ genpkg() {
 		${_alternatives:+--alternatives "${_alternatives}"} \
 		${_preserve:+--preserve} \
 		${tags:+--tags "${tags}"} \
+		${changelog:+--changelog "${changelog}"} \
 		--architecture ${arch} \
 		--homepage "${homepage}" \
 		--license "${license}" \

common/xbps-src/shutils/show.sh

@@ -15,6 +15,7 @@ show_pkg() {
     [ -n "$noarch" ] && echo "noarch:		yes"
     echo "maintainer:	$maintainer"
     [ -n "$homepage" ] && echo "Upstream URL:	$homepage"
+    [ -n "$changelog" ] && echo "Changelog URL:	$changelog"
     [ -n "$license" ] && echo "License(s):	$license"
     [ -n "$build_style" ] && echo "build_style:	$build_style"
     for i in ${configure_args}; do