[API] Add version macros and functions

Step version up to 0.5.0.

Also, fix to pass "make distcheck"

src/Makefile.am

diff --git a/src/Makefile.am b/src/Makefile.am
index 0a7edb3..73ac547 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -2,6 +2,9 @@
 
 NULL =
 EXTRA_DIST =
+CLEANFILES =
+DISTCLEANFILES =
+MAINTAINERCLEANFILES =
 
 # The following warning options are useful for debugging: -Wpadded -Wcast-align
 #AM_CXXFLAGS =
@@ -35,6 +38,7 @@
 	hb-font.h \
 	hb-shape.h \
 	hb-unicode.h \
+	hb-version.h \
 	$(NULL)
 
 HBSOURCES += \
@@ -61,6 +65,10 @@
 	hb-ot-tag.h \
 	$(NULL)
 
+MAINTAINERCLEANFILES = \
+	$(srcdir)/hb-version.h \
+	$(NULL)
+
 if HAVE_GLIB
 HBCFLAGS += $(GLIB_CFLAGS)
 HBLIBS   += $(GLIB_LIBS)
@@ -99,6 +107,7 @@
 libharfbuzz_la_CPPFLAGS = $(HBCFLAGS)
 libharfbuzz_la_LIBADD = $(HBLIBS)
 pkginclude_HEADERS = $(HBHEADERS)
+nodist_pkginclude_HEADERS = hb-version.h
 
 
 GENERATORS = \