Move python specific into PY subdirectories

Change logic to provide both python2 and python3 in PYTHON variable.
If set to empty, nothing is built. If set to specific, only that is
built. Simplify logic. Makes a bit uglier error reports when something
fails.

Makefile

@@ -9,8 +9,7 @@ SIZE         = $(CROSS_PREFIX)size
 STRIP        = $(CROSS_PREFIX)strip
 SHLIB        = $(CC) -shared
 STRIPLIB     = $(STRIP) --strip-unneeded
-SWIG         = swig
-PYTHON      ?= -all-
+PYTHON      ?= python2 python3
 
 SOVERSION    = 1
 
@@ -77,7 +76,7 @@ DOCS = \
 
 LIB = $(LIB_LGPIO) $(LIB_RGPIO)
 
-ALL = $(LIB) rgpiod rgs DOC/.docs
+ALL = $(LIB) rgpiod rgs DOC/.docs lgpio.py
 
 LINK_LGPIO  = -L. -llgpio -pthread -lrt
 LINK_RGPIO  = -L. -lrgpio -pthread -lrt
@@ -101,6 +100,13 @@ DOC/.docs: $(DOCS)
 	@[ -d "DOC" ] && cd DOC && ./cdoc || echo "*** No DOC directory ***"
 	touch DOC/.docs
 
+lgpio.py: $(LIB_LGPIO)
+	@for PBIN in $(PYTHON); do \
+		if $$PBIN --version >&/dev/null; then \
+			$(MAKE) -C PY_LGPIO build-python PYTHON=$$PBIN $(MAKEFLAGS) || \
+			echo "*** build of $$PBIN lgpio.py failed ***"; \
+		fi; \
+	done
 clean:
 	rm -f *.o *.i *.s *~ $(ALL) *.so.$(SOVERSION)
 
@@ -137,25 +143,18 @@ ifeq ($(DESTDIR),)
 	ldconfig
 endif
 
-install-python:
-	(cd PY_RGPIO && $(PYTHON) setup.py -q install $(PYINSTALLARGS)) || echo "*** install of Python rgpio.py failed ***";
-	if type -p $(SWIG) >&/dev/null; then \
-		(cd PY_LGPIO && $(SWIG) -python lgpio.i) || echo "*** need swig package to install lgpio.py ***"; \
-		(cd PY_LGPIO && \
-		$(PYTHON) setup.py build_ext $(PYBUILDARGS) && \
-		$(PYTHON) setup.py -q install $(PYINSTALLARGS) ) || \
-		echo "*** install of Python lgpio.py failed ***"; \
-	fi
+install-python: lgpio.py
+	$(MAKE) -C PY_LGPIO install $(MAKEFLAGS)
+	$(MAKE) -C PY_RGPIO install $(MAKEFLAGS)
 
 install: $(ALL) install-native
-	if [ "$(PYTHON)" = '-all-' ]; then \
-		python2 --version >&/dev/null && \
-		$(MAKE) install-python PYTHON=python2 $(MAKEFLAGS); \
-		python3 --version >&/dev/null && \
-		$(MAKE) install-python PYTHON=python3 $(MAKEFLAGS); \
-	elif [ -n "$(PYTHON)" ]; then \
-		$(MAKE) install-python $(MAKEFLAGS); \
-	fi
+	@for PBIN in $(PYTHON); do \
+		if $$PBIN --version >&/dev/null; then \
+			$(MAKE) -C PY_RGPIO install PYTHON=$$PBIN $(MAKEFLAGS) && \
+			$(MAKE) -C PY_LGPIO install PYTHON=$$PBIN $(MAKEFLAGS) || \
+			echo "*** install of $$PBIN modules failed ***"; \
+		fi; \
+	done
 
 uninstall:
 	rm -f $(DESTDIR)$(includedir)/lgpio.h

PY_LGPIO/Makefile

@@ -0,0 +1,32 @@
+SWIG         = swig
+PYTHON      ?= python3
+
+ifeq ($(DESTDIR),)
+  PYBUILDARGS =
+  PYINSTALLARGS =
+else
+  PYBUILDARGS = --include-dirs=$(DESTDIR)$(includedir) --library-dirs=$(DESTDIR)$(libdir)
+  PYINSTALLARGS = --root=$(DESTDIR)
+endif
+
+all: build-python
+
+build-python: lgpio.i
+	@if type -p $(SWIG) >&/dev/null; then \
+		$(SWIG) -python lgpio.i; \
+		$(PYTHON) setup.py build_ext $(PYBUILDARGS); \
+	else \
+		echo "*** need swig package to install lgpio.py ***"; \
+	fi
+
+lgpio_wrap.c: build-python
+
+install-python:
+	@if type -p $(SWIG) >&/dev/null; then \
+		$(PYTHON) setup.py -q install $(PYINSTALLARGS); \
+	fi
+
+install: install-python
+
+clean:
+	rm -f lgpio_wrap.c

PY_RGPIO/Makefile

@@ -0,0 +1,17 @@
+PYTHON      ?= python3
+
+ifeq ($(DESTDIR),)
+  PYINSTALLARGS =
+else
+  PYINSTALLARGS = --root=$(DESTDIR)
+endif
+
+all: build-python
+
+build-python:
+	@$(PYTHON) setup.py build
+
+install-python: build-python
+	@$(PYTHON) setup.py -q install $(PYINSTALLARGS)
+
+install: install-python