Got all the header parsing and matching working.

Altered core logic to just be:
	- rules that run before a global filters
	- N global filter(s)
	- rules that run after filters

All steps are optional.

FossilOrigin-Name: 250b5d22e0387865e13a4adee9dadd122583311bde1d015eefb3321c525827be

config.yml

@@ -5,14 +5,19 @@
 # Default, no logging.  Relative to homedir.
 #logfile: sieb.log
 
-## Filter message before rules
-pre_filter:
-  - 'reformail -A "X-Sieb: Pre-filtered!"'
-#  - bogofilter
+## Rules tried before global filtering
+early_rules:
+  -
+    headers:
+      to: mahlon@(laika|ravn)
+      received: .*sendgrid.*
+    filter:
+      - [ reformail, -A, "X-Sieb: This matched." ]
+    deliver: .whatever
 
-## Filter message after rules
-#post_filter:
-#  - bogofilter
+## Filter message before additional rules.
+filter:
+  - [ reformail, -A, "X-Sieb: That shit totally matched" ]
 
 ## Ordered, top down, first match wins.
 ## Headers are lowercased.  Multiple matches are AND'ed.
@@ -20,12 +25,12 @@ pre_filter:
 ## Delivery default is ~/Maildir, any set value is an auto-created maildir under
 ## that path.
 ##
-rules:
-  -
-    headers:
-      x-what: pcre-matcher
-      poonie: pcre-matcher
-    deliver: .whatever
+# rules:
+#   -
+#     headers:
+#       x-what: pcre-matcher
+#       poonie: pcre-matcher
+#     deliver: .whatever
 
   # # Magic "TO" which means To: OR Cc:
   # -