Refactor tags (#269)

* Standardize disabling of Gollum tags per format
* Check tag format instead of trying to parse every tag as every kind of link
* More refactoring

* Fix errors

* Don't implicitly assume tag links are relative to the wiki root

* Fix image tags

* Fix include directive and tests

* Refactor

* Add regression test for File links without description

* New generic approach to skipping filters for specific formats

* Implement generic tag skipping in Markup instead of Filter class

* Add tests. Remove Markup#render_default

lib/gollum-lib/filter.rb

@@ -55,12 +55,12 @@ def initialize(markup)
       @map    = {}
     end
 
-    def extract(_d)
+    def extract(data)
       raise RuntimeError,
             "#{self.class} has not implemented ##extract!"
     end
 
-    def process(_d)
+    def process(data)
       raise RuntimeError,
             "#{self.class} has not implemented ##process!"
     end

lib/gollum-lib/filter/code.rb

@@ -6,8 +6,6 @@
 class Gollum::Filter::Code < Gollum::Filter
   def extract(data)
     case @markup.format
-    when :txt
-      return data
     when :asciidoc
       data.gsub!(/^(\[source,([^\r\n]*)\]\n)?----\n(.+?)\n----$/m) do
         cache_codeblock(Regexp.last_match[2], Regexp.last_match[3])

lib/gollum-lib/filter/plain_text.rb

@@ -6,6 +6,10 @@
 
 class Gollum::Filter::PlainText < Gollum::Filter
 
+    def do_process(_d)
+      skip? ? _d : process(_d)
+    end
+
   def extract(data)
     @markup.format == :txt ? "<pre>#{CGI.escapeHTML(data)}</pre>" : data
   end

lib/gollum-lib/filter/plantuml.rb

@@ -69,7 +69,6 @@ def self.configure
   # Extract all sequence diagram blocks into the map and replace with
   # placeholders.
   def extract(data)
-    return data if @markup.format == :txt
     data.gsub(/(@startuml\r?\n.+?\r?\n@enduml\r?$)/m) do
       id       = Digest::SHA1.hexdigest($1)
       @map[id] = { :code => $1 }

lib/gollum-lib/filter/remote_code.rb

@@ -13,7 +13,6 @@
 #
 class Gollum::Filter::RemoteCode < Gollum::Filter
   def extract(data)
-    return data if @markup.format == :txt
     data.gsub(/^[ \t]*``` ?([^:\n\r]+):((http)?[^`\n\r]+)```/) do
       language = Regexp.last_match[1]
       uri      = Regexp.last_match[2]