Add underscore (#149)

Author: MDLC01

CHANGELOG.md

@@ -8,6 +8,9 @@
 
 ### New in `sym`
 
+- Punctuation
+  - `underscore`: _
+
 - Mathematical symbols
   - `emptyset.zero`: ∅︀
   - `nothing.zero`: ∅︀

src/modules/sym.txt

@@ -144,6 +144,7 @@ dash
   .o ⊝
   .wave 〜
   .wave.double 〰\vs{text}
+underscore _
 dot
   .op ⋅
   .basic \u{2E}