recognize Harbour sources

[Harbour language: https://github.com/harbour/core]

Reopened PR 593 with the two language additions split off.

lib/linguist/languages.yml

@@ -643,6 +643,12 @@ Handlebars:
   - .html.handlebars
   - .html.hbs
 
+Harbour:
+  type: programming
+  lexer: Text only
+  color: "#0e60e3"
+  primary_extension: .hb
+ 
 Haskell:
   type: programming
   color: "#29b544"