docs: Split out the ASCII-IPA ':' character into a suprasegmentals section and document the stress markers.

docs/phonemes/kirshenbaum.md

 - [Vowels](#vowels)
   - [Other Symbols](#other-symbols-1)
 - [Diacritics](#diacritics)
+- [Suprasegmentals](#suprasegmentals)
+  - [Stress](#stress)
+  - [Length](#length)
 - [References](#references)
 
 ----------
 
 | Symbol | Feature |
 |--------|---------|
-| `:`    | `{lng}` |
 | `!`    | `{clk}` |
 | `[`    | `{dnt}` |
 | `;`    | `{pzd}` |
 |---------|-----------|---------|
 | `` ` `` | `{ejc}`   | `{imp}` |
 
+## Suprasegmentals
+
+### Stress
+
+| Symbol | Name             |
+|--------|------------------|
+| `'`    | primary stress   |
+| `,`    | secondary stress |
+
+### Length
+
+| Symbol | Feature |
+|--------|---------|
+| `:`    | `{lng}` |
+
 ## References
 
 1. <a name="ref1"></a> Kirshenbaum, Evan,