Sidebar work: added collapsing categories

Big refactoring of SCSS

active state for sidebar links

update gitignore for node_modules folder

removing node_modules from index

Sticky Liquid link in sidebar

Cleaned up index page

Adding fixed width to buttons

Refactoring

Converted sidebar to use Collections

Refactor sidebar CSS

_objects/join.md

@@ -0,0 +1,11 @@
+---
+title: join
+---
+
+`join` joins the elements of an array, using the character you provide.
+
+| Code                                                   | Output             |
+|-------------------------------------------------------:|:-------------------|
+| {% raw %}`{{ product.tags | join: ', ' }}`{% endraw %}     | `"sale, mens, womens, awesome` |
+
+In the sample above, assume that `product.tags` resolves to: `["sale", "mens", "womens", "awesome"]`.

_objects/last.md

@@ -0,0 +1,11 @@
+---
+title: last
+---
+
+Return the last element of an array.
+
+| Code                                                   | Output             |
+|-------------------------------------------------------:|:-------------------|
+| {% raw %}`{{ product.tags | last }}`{% endraw %}     | `"awesome"` |
+
+In the sample above, assume that `product.tags` resolves to: `["sale", "mens", "womens", "awesome"]`.

_objects/lstrip.md

@@ -0,0 +1,9 @@
+---
+title: lstrip
+---
+
+Strips all whitespace (tabs, spaces, and newlines) from the left side of a string.
+
+| Code                                                   | Output             |
+|-------------------------------------------------------:|:-------------------|
+| {% raw %}`{{ '   too many spaces   ' | lstrip }}`{% endraw %}     | `"too many spaces   "` |