mail: Add basic filtering system

imapfilter now looks for account information in an accounts.lua file in
its configuration directory -- the file should return account
information as a table with each account being a top-level entry in the
table.

A sample spam-moving script has been supplied:
For now, it will take a list of sender addresses and put everything in
the list from the inbox into the dump directory.

An example list of senders has been supplied for testing purposes, but
this should eventually be read from a file containing an extensible list
of senders (and perhaps even different properties such as subject, etc.)

The imapfilter xdg alias has been fixed.

Coherence between the imap folder structure and notmuch tagging system
still has to be achieved -- either by aerc using the folder structure as
a query map, or notmuch tags automatically being applied for specific
imap filtering options.

mail/.local/bin/checkmail

@@ -12,12 +12,9 @@
 # https://sourceforge.net/p/isync/feature-requests/8/
 
 MBSYNC_MAX_TRIES=3
-MBSYNC_PRE="imapfilter"
+MBSYNC_PRE="imapfilter -c /home/marty/.config/imapfilter/config.lua"
 MBSYNC_POST="notmuch new"
 
-success="false"
-tries=0
-
 # fail the routine and optionally send a message why
 fail() {
   [ -n "$1" ] && echo "$1"
@@ -43,15 +40,23 @@ if [ "$1" = "raw" ]; then
   exit
 fi
 
-$MBSYNC_PRE
-while true; do
-  if checkmail; then
-    success="true"
-  fi
+main() {
+  $MBSYNC_PRE
 
-  if [ $success = "true" ] || [ $tries -gt $MBSYNC_MAX_TRIES ]; then
-    fail "Maximum retries reached unsuccessfully."
-  fi
-  tries=$((tries + 1))
-done
-$MBSYNC_POST
+  tries=0
+  while true; do
+    if checkmail; then
+      break
+    fi
+
+    tries=$((tries + 1))
+    if [ $tries -gt $MBSYNC_MAX_TRIES ]; then
+      fail "maximum retries reached without success."
+    fi
+  done
+  unset tries
+
+  $MBSYNC_POST
+}
+
+main