Enhancement - #363 export.ical

- Added feature #363 supporting iCalendar export via the 'export.ical'
  command.
- Updated documentation.
- Removed unnecessary localization of canonical command names.

i18n/strings.en-US

@@ -40,10 +40,9 @@
 208 done
 209 duplicate
 210 edit
-211 export
+
 212 help
-213 history.monthly
-214 ghistory.monthly
+
 215 import
 216 info
 217 prepend
@@ -60,8 +59,6 @@
 228 version
 229 shell
 230 config
-231 history.annual
-232 ghistory.annual
 
 # 3xx Attributes - must be sequential
 300 project