Enable conversion of (some) standard TEI P5

Providing an option --xmlid-to-textsigle
to convert P5 xml:id attributes to three part I5-sigles

Resolves #4
Resolves #5

Change-Id: I8fd23b7021c25cf4d80234a0570d06dea78e7813
diff --git a/Readme.pod b/Readme.pod
index 5dff430..b214dce 100644
--- a/Readme.pod
+++ b/Readme.pod
@@ -152,6 +152,21 @@
 Expects a comma-separated list of tags to be ignored when the structure
 is parsed. Content of these tags however will be processed.
 
+=item B<--xmlid-to-textsigle> <from-regex>@<to-c/to-d/to-t>
+
+Expects a regular replacement expression (separated by a B<@> between the
+search and the replacement) to convert text id attributes to text sigles
+with three parts (separated by B</>).
+
+Example:
+
+  tei2korapxml  \
+    --xmlid-to-textsigle 'ICC.German\.([^.]+\.[^.]+)\.(.+)@ICCGER/$1/$2' \
+    -tk - < t/data/icc_german_sample.p5.xml
+
+Converts text id `ICC.German.DeReKo.WPD17.G11.00238' to
+sigle `ICCGER/DeReKo.WPD17/G11.00238'.
+
 =item B<--inline-tokens> <foundry>#[<file>]
 
 Define the foundry and file (without extension)