make: Further improve build time

This commit sees several improvements to the build performance:

- Introduce cache.mk, which creates makefiles caching often used
  variables, per tree and per project.
- Define more variables with := enclosed in condistions, instead of
  defining them with ?=, because the RHS of ?= is expanded deferredly.
- Add more definitions for executables.
- Move some more specialized definitions out into specialized makefiles,
  notably htdocs.mk and tmpl.mk

Signed-off-by: Jan Lindemann <jan@janware.com>

make/htdocs.mk

@@ -3,6 +3,22 @@ LESS_GENERATED_CSS        ?= $(patsubst %.less,%.css,$(LESS_SRC))
 LESS_CPY                  ?= lesscpy
 
 include $(MODDIR)/make/defs.mk
+
+# -- HTML
+INSTALLATION_FILE_TYPES  += HTML
+BUILD_HTMLDIR             = $(TOPDIR)/htdocs
+LOCAL_HTML               += $(filter-out $(DONT_INSTALL),$(wildcard *.html *.css *.php *.js) $(FONTS) $(IMAGES))
+ifeq ($(HTML_SUBDIR),)
+  HTML_SUBDIR            := $(shell $(PWD) | $(SED) '/.*\/htdocs\(\/\|$$\)/!d; s%.*/htdocs\(/\|$$\)%%')
+endif
+ifeq ($(HTML_SUBDIR),)
+  INSTALL_HTMLDIR        ?= $(PROJECT_HTMLDIR)
+else
+  INSTALL_HTMLDIR        ?= $(PROJECT_HTMLDIR)/$(HTML_SUBDIR)
+endif
+INSTALLED_HTML           += $(addprefix $(INSTALL_HTMLDIR)/,$(LOCAL_HTML))
+
+
 include $(MODDIR)/make/js.mk
 include $(MODDIR)/make/rules.mk
 include $(MODDIR)/make/dev-utils.mk