Makefile: have docdir behave the way the GNU standards say.

I had

    docdir = $(datarootdir)/doc
    pkgdocdir = $(docdir)/libretools
    # install docs to $(pkgdocdir)

but the GNU Coding Standards (July 25, 2016 revision), say I should be
doing

    docdir = $(datarootdir)/doc/libretools
    # install docs to $(docdir)

As the config.mk states, we aren't a GNU package.  But let's still follow
their standards here, to follow the principle of least surprise.

4 files changed, 2 insertions, 5 deletions

diff --git a/build-aux/Makefile.each.head/20-libretools.mk b/build-aux/Makefile.each.head/20-libretools.mk
index 20abd8b..be4b8aa 100644
--- a/build-aux/Makefile.each.head/20-libretools.mk
+++ b/build-aux/Makefile.each.head/20-libretools.mk
@@ -14,7 +14,6 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 pkgconfdir    = $(sysconfdir)/libretools.d
-pkgdocdir     = $(docdir)/libretools
 pkglibexecdir = $(libexecdir)/libretools
 
 # Auto-detect ########################################################
diff --git a/build-aux/Makefile.each.tail/20-libretools.mk b/build-aux/Makefile.each.tail/20-libretools.mk
index 49e8fb8..4398e2c 100644
--- a/build-aux/Makefile.each.tail/20-libretools.mk
+++ b/build-aux/Makefile.each.tail/20-libretools.mk
@@ -26,7 +26,7 @@ files.out.all += $(filter-out $(files.src),$(libretools.out)) \
 files.sys.all += $(addprefix $(bindir)/,$(libretools.out.bins)) \
                  $(addprefix $(pkgconfdir)/,$(libretools.out.confs)) \
                  $(addprefix $(pkglibexecdir)/,$(libretools.out.libexecs) $(libretools.out.libs)) \
-                 $(addprefix $(pkgdocdir)/,$(libretools.out.docs)) \
+                 $(addprefix $(docdir)/,$(libretools.out.docs)) \
                  $(addprefix $(mandir)/man1/,$(filter %.1,$(libretools.out.mans))) \
                  $(addprefix $(mandir)/man2/,$(filter %.2,$(libretools.out.mans))) \
                  $(addprefix $(mandir)/man3/,$(filter %.3,$(libretools.out.mans))) \
@@ -61,7 +61,7 @@ $(outdir)/everything.pot: $(addprefix $(outdir)/,$(addsuffix .pot,$(libretools.p
 
 # Install rules ######################################################
 $(DESTDIR)$(pkgconfdir)/%   : $(outdir)/%  ; install -T -Dm644 '$<' '$@'
-$(DESTDIR)$(pkgdocdir)/%    : $(outdir)/%  ; install -T -Dm644 '$<' '$@'
+$(DESTDIR)$(docdir)/%       : $(outdir)/%  ; install -T -Dm644 '$<' '$@'
 $(DESTDIR)$(mandir)/man1/%.1: $(outdir)/%.1; install -T -Dm644 '$<' '$@'
 $(DESTDIR)$(mandir)/man2/%.2: $(outdir)/%.2; install -T -Dm644 '$<' '$@'
 $(DESTDIR)$(mandir)/man3/%.3: $(outdir)/%.3; install -T -Dm644 '$<' '$@'
diff --git a/build-aux/Makefile.once.head/00-libretools.mk b/build-aux/Makefile.once.head/00-libretools.mk
index 1f2957d..7c1ffef 100644
--- a/build-aux/Makefile.once.head/00-libretools.mk
+++ b/build-aux/Makefile.once.head/00-libretools.mk
@@ -18,7 +18,6 @@ define mod.libretools.doc
 # Inputs:
 #   - Install paths (Directory variables): 
 #     - `pkgconfdir    = $(sysconfdir)/libretools.d`
-#     - `pkgdocdir     = $(docdir)/libretools`
 #     - `pkglibexecdir = $(libexecdir)/libretools`
 #   - Outputs (Directory variables): 
 #     - `libretools.out.mans`
diff --git a/config.mk b/config.mk
index 0d564e0..882e2e9 100644
--- a/config.mk
+++ b/config.mk
@@ -26,7 +26,6 @@ datadir     = $(datarootdir)
 #sysconfdir  = $(prefix)/etc
 sysconfdir  = /etc
 
-docdir = $(datarootdir)/doc
 mandir = $(datarootdir)/man
 
 devtoolsdir = $(call abspath,$(topsrcdir)/../devtools-par)