Add abs filter docs

filters/abs.md

@@ -0,0 +1,37 @@
+---
+title: abs
+---
+
+Returns the absolute value of a number.
+
+```liquid
+{% raw %}
+{{ -17 | abs }}
+{% endraw %}
+```
+
+```text
+17
+```
+
+```liquid
+{% raw %}
+{{ 4 | abs }}
+{% endraw %}
+```
+
+```text
+4
+```
+
+`abs` will work on a string if the string only contains a number.
+
+```liquid
+{% raw %}
+{{ "-19.86" | abs }}
+{% endraw %}
+```
+
+```text
+19.86
+```