Add build.header.c

A new module type for creating just a header file. This is useful for e.g.
shared interfaces and so on which are not backed by a library.

scripts/build.header.c/build.install-header

@@ -0,0 +1,12 @@
+build_target @NAME@
+
+# make paths (this is for Gentoo in particular)
+build_dir_tree "${INCLUDEDIR}" || return 1
+
+# install header
+echo "Installing header file '${@CNAME@_HEADER}' into ${INCLUDEDIR}"
+install_header ${@CNAME@_HEADER} ${INCLUDEDIR} 0644 || return 1
+
+print_success "Done"
+
+# vim: syntax=sh:@VIM_MODELINE@