chore(meta): change labels of severity to category (#3488)

Author: seanmonstar

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: "Bug report \U0001F41B"
 about: Create a report to help us improve
 title: ''
-labels: S-bug
+labels: C-bug
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/feature_request.md

@@ -2,7 +2,7 @@
 name: "Feature request \U0001F4A1"
 about: Suggest an idea for this project
 title: ''
-labels: S-feature
+labels: C-feature
 assignees: ''
 
 ---

docs/ISSUES.md

@@ -91,6 +91,16 @@ These labels indicate an issue is "blocked" for some reason.
 - **B-rfc**: request for comments. More discussion is needed to explore the design.
 - **B-upstream**: waiting on something in a dependency or the compiler.
 
+### Category
+
+The category marks what kind of issue this is.
+
+- **C-bug**: something is wrong, this is bad!
+- **C-feature**: this is a new feature request, adding something new.
+- **C-performance**: make existing working code go faster.
+- **C-refactor**: improve internal code to help readability and maintenance.
+- **C-chore**: a general chore or maintenance task.
+
 ### Effort
 
 The effort labels are a best-guess at roughly how much effort and knowledge of hyper is needed to accomplish the task.
@@ -99,14 +109,6 @@ The effort labels are a best-guess at roughly how much effort and knowledge of h
 - **E-medium**: some knowledge of how hyper internals work would be useful.
 - **E-hard**: likely requires a deeper understanding of how hyper internals work.
 
-### Severity
-
-The severity marks how _severe_ the issue is. Note this isn't "importance" or "priority".
-
-- **S-bug**: something is wrong, this is bad!
-- **S-feature**: this is a new feature request, adding something new.
-- **S-performance**: make existing working code go faster.
-- **S-refactor**: improve internal code to help readability and maintenance.
 
 [issues]: https://github.com/hyperium/hyper/issues
 [COC]: ./CODE_OF_CONDUCT.md