docs/phonemes.md: restructure the syllabicity features.

docs/phoneme_model.md

 - [Vowel Backness](#vowel-backness)
 - [Rounding and Labialization](#rounding-and-labialization)
   - [Vowel Rounding](#vowel-rounding)
+- [Syllabicity](#syllabicity)
 - [References](#references)
 
 ----------
 | unrounded | `unr`   | `unr`                                    |
 | rounded   | `rnd`   | `ptr` if `bck` or `cnt`; `cmp` if `fnt`. |
 
+## Syllabicity
+
+| Feature | Name         |
+|---------|--------------|
+| `syl`   | syllabic     |
+| `nsy`   | non-syllabic |
+
 ## References
 
 1. <a name="ref1"></a> Kirshenbaum, Evan,

docs/phonemes.md

   - [Air Flow](#air-flow)
   - [Phonation](#phonation)
   - [Rounding and Labialization](#rounding-and-labialization)
-- [Features](#features)
   - [Syllabicity](#syllabicity)
+- [Features](#features)
   - [Consonant Release](#consonant-release)
   - [Fortis and Lenis](#fortis-and-lenis)
   - [Co-articulation](#co-articulation-1)
 | `mrd`   | ◌̹      | more rounded |
 | `lrd`   | ◌̜      | less rounded |
 
-## Features
-
 ### Syllabicity
 
 | Feature | Symbol | Name            |
 | `syl`   | ◌̩      | syllabic        |
 | `nsy`   | ◌̯      | non-syllabic    |
 
+## Features
+
 ### Consonant Release
 
 | Feature | Symbol | Name                            |