Added rule to build html doc.

Also had to change the dtd and stylesheet url's to http as xsltproc does
not recognize https (tries to look it up as a file).

And removed the checked in html doc since A) it's generated, and B) is
available in the gh-pages branch.

Makefile

@@ -5,6 +5,7 @@
 
 #   the used tools
 APXS=apxs
+XSLT=xsltproc
 
 #   the default target
 all: .libs/mod_proxy_protocol.so
@@ -17,6 +18,12 @@ all: .libs/mod_proxy_protocol.so
 install: .libs/mod_proxy_protocol.so
 	$(APXS) -i mod_proxy_protocol.c
 
+# generate the html doc
+docs: mod_proxy_protocol.html
+
+mod_proxy_protocol.html: mod_proxy_protocol.xml mod_proxy_protocol.xml.meta
+	$(XSLT) -o $@ $<
+
 #   cleanup
 clean:
-	-rm -rf mod_proxy_protocol.o mod_proxy_protocol.lo mod_proxy_protocol.slo mod_proxy_protocol.la .libs
+	-rm -rf mod_proxy_protocol.o mod_proxy_protocol.lo mod_proxy_protocol.slo mod_proxy_protocol.la .libs mod_proxy_protocol.html

mod_proxy_protocol.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
-<!DOCTYPE modulesynopsis SYSTEM "https://httpd.apache.org/docs/2.4/style/modulesynopsis.dtd">
-<?xml-stylesheet type="text/xsl" href="https://httpd.apache.org/docs/2.4/style/manual.en.xsl"?>
+<!DOCTYPE modulesynopsis SYSTEM "http://httpd.apache.org/docs/2.4/style/modulesynopsis.dtd">
+<?xml-stylesheet type="text/xsl" href="http://httpd.apache.org/docs/2.4/style/manual.en.xsl"?>
 
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