Add Idris.

This adds Idris into the mix and uses the text-only parser for now, pending
upstream merging this patch in:
https://bitbucket.org/birkenfeld/pygments-main/pull-request/210/idris-lexer-added-lexer-for-idris/diff

Once that gets merged in, the lexer should change to idris.

lib/linguist/languages.yml

@@ -628,6 +628,13 @@ INI:
   - .properties
   primary_extension: .ini
 
+Idris:
+  type: programming
+  lexer: Text only
+  primary_extension: .idr
+  extensions:
+  - .lidr
+
 Inno Setup:
   primary_extension: .iss
   lexer: Text only