Move templates outside the source .mk filestemplates

Templates now no longer use Make variables for substitution
but instead replace strings with their equivalent:

  template_name: Corresponds to n=template_name
  project_name:  Corresponds to $(PROJECT) or in=project_name

This allows defining templates outside of Makefiles. For
example an external plugin could define their templates
in templates/my_template.erl and then have the following
in the included Makefile:

  tpl_my_template = $(file < $(THIS)/templates/my_template.erl)

By default the created file will be in src/template_name.erl.
This can be overriden with the tplp_* variable:

  tplp_my_template = src/model/my_template.erl

Substitution is applied both to the template contents and
to its path.

In addition, attempting to overwrite an existing file when
creating a template will result in failure.

1 files changed, 8 insertions, 0 deletions

diff --git a/CHANGELOG.asciidoc b/CHANGELOG.asciidoc
index 863780e..0261b82 100644
--- a/CHANGELOG.asciidoc
+++ b/CHANGELOG.asciidoc
@@ -43,3 +43,11 @@
             without an explicit fetch method). Adding "git"
             at the beginning of the dep line is the modern
             equivalent.
+
+2024/11/22: Templates no longer use Make variables for
+            substitution. Instead the strings template_name
+            and project_name get replaced by their equivalent.
+            Note that using variables in your own templates
+            should still work, but that this way of doing
+            things is deprecated. This change makes it
+            possible to have templates outside of Makefiles.