Add x:rep labels for awarding reputation (#196)

Up until now, we used the `x:size` label to deviate from the default reputation that is awarded for a pull request.
This worked well, until we decided to also allow awarding reputation for opening an issue (but only for large/massive issues), as we already used the `x:size` label for an indication of the effort needed to implement said issue.
To combat this, we decided to switch to using a `x:rep` label for awarding reputation, both for pull requests _and_ issues.
This PR adds the `x:rep` labels.

For backwards compatibility purposes, we still support the `x:size` label on pull requests, but recommend using the `x:rep` label from now on.

For more information on reputation and how these labels should be used, check out https://exercism.org/docs/using/product/reputation

global-files/.github/labels.yml

@@ -86,6 +86,30 @@
   description: "Work on Test Runners"
   color: "ffffff"
 
+# The `x:rep/<value>` labels describe the amount of reputation to award
+# 
+# For more information on reputation and how these labels should be used,
+# check out https://exercism.org/docs/using/product/reputation
+- name: "x:rep/tiny"
+  description: "Tiny amount of reputation"
+  color: "ffffff"
+
+- name: "x:rep/small"
+  description: "Small amount of reputation"
+  color: "ffffff"
+
+- name: "x:rep/medium"
+  description: "Medium amount of reputation"
+  color: "ffffff"
+
+- name: "x:rep/large"
+  description: "Large amount of reputation"
+  color: "ffffff"
+
+- name: "x:rep/massive"
+  description: "Massive amount of reputation"
+  color: "ffffff"
+
 # The `x:size/<value>` labels describe the expected amount of work for a contributor
 - name: "x:size/tiny"
   description: "Tiny amount of work"