Regex: support more grouping functions

In case of multiple matches we only had an option to return a sum of
numeric values. Add more functions.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

TUTORIAL.md

@@ -91,8 +91,9 @@ Optional properties:
 
 - `type` (if present must be one of: `int`, `float`, `date`) -results
   in parsing every matched value to a specified type
-- `group` (if present must be `sum`) - results in grouping all matched
-  values using specified method
+- `group` (if present must be one of: `sum`, `min`, `max`, `first`,
+  `last`) - specifies grouping function (defines what value to return in
+  case of multiple matches)
 
 Example for `regex`:
 

src/invoice2data/extract/parsers/regex.py

@@ -46,6 +46,14 @@ def parse(template, field, settings, content, legacy=False):
     if "group" in settings:
         if settings["group"] == "sum":
             result = sum(result)
+        elif settings["group"] == "min":
+            result = min(result)
+        elif settings["group"] == "max":
+            result = max(result)
+        elif settings["group"] == "first":
+            result = result[0]
+        elif settings["group"] == "last":
+            result = result[-1]
         else:
             logger.warning("Unsupported grouping method: " + settings["group"])
             return None