Add colspan support

This adds support for having colspan generated in tables. The spec is yet to be updated with GFM.

A cell with the sole contents of `-` will be ignored, and previous cells in the row will have a colspan attribute.

Side effect would be that users can't have a cell with just `-` in it.

Fixes GovReady#10

commonmark_extensions/tables.py

@@ -171,7 +171,7 @@ def inner_parser(cell):
         for part in table_parts:
             for row in part:
                 for i, cell in enumerate(row):
-                    row[i] = inner_parser(cell)
+                    row[i] = inner_parser(cell) if cell != "-" else None
 
         # Store the parsed table on the node.
         block.column_properties = column_properties
@@ -211,6 +211,9 @@ def table(self, node, entering):
                 for row in part:
                     self.lit("<tr>\n")
                     for colidx, cell in enumerate(row):
+                        if cell is None:
+                            continue
+
                         if part_tag == "thead":
                             col_tag = "th"
                             if self.options.get("table_th_scope"):
@@ -224,6 +227,15 @@ def table(self, node, entering):
                         if colidx in node.column_properties and "align" in node.column_properties[colidx]:
                             col_attrs += ' align=\"' + node.column_properties[colidx]["align"] + "\""
 
+                        span = 1
+                        for nextid in range(colidx+1, len(row)):
+                            if row[nextid] is None:
+                                span += 1
+                            else:
+                                break
+                        if span > 1:
+                            col_attrs += ' colspan=\"' + str(span) + '\"'
+
                         self.lit("<" + col_tag + col_attrs + ">")
 
                         import copy