Fix several it's -> its in error messages and docs (#765)

Author: Omnikar

changelog.md

@@ -885,7 +885,7 @@ You can find the release announcement [here](https://uiua.org/blog/uiua-0.10.0).
   - The behavior of [`content ◇`](https://uiua.org/docs/content) is less implicit and is not prone to some of the potential unexpected behavior of [`unpack ⊐`](https://uiua.org/docs/unpack)
 - Add the [`unique ◰`](https://uiua.org/docs/unique) function, which creates a mask of the first occurrence of each unique value in an array
   - Change [`deduplicate ◴`](https://uiua.org/docs/deduplicate)'s glyph to reflect its relationship with [`unique ◰`](https://uiua.org/docs/unique). Code using `⊖` will continue to work and will be formatted as `◴`.
-- [`table ⊞`](https://uiua.org/docs/table) now works on rows of arrays but keeps it's optimizations for lists
+- [`table ⊞`](https://uiua.org/docs/table) now works on rows of arrays but keeps its optimizations for lists
   - You never wanted element-wise combinations of multi-dimensional arrays anyway
   - Deprecate [`cross ⊠`](https://uiua.org/docs/cross), as it is now redundant
   - This is technically a breaking change, but it is unlikely to break much code

src/algorithm/media.rs

@@ -917,7 +917,7 @@ pub(crate) fn voxels(val: &Value, env: &mut Uiua) -> UiuaResult<Value> {
                     [r, g, b] => fog = Some([r, g, b]),
                     _ => {
                         return Err(env.error(format!(
-                            "Fog must be a scalar or list of 3 numbers, but it's shape is {}",
+                            "Fog must be a scalar or list of 3 numbers, but its shape is {}",
                             arg.shape
                         )))
                     }
@@ -930,7 +930,7 @@ pub(crate) fn voxels(val: &Value, env: &mut Uiua) -> UiuaResult<Value> {
                     pos = Some([x, y, z]);
                 } else {
                     return Err(env.error(format!(
-                        "Camera position must be 3 numbers, but it's shape is {}",
+                        "Camera position must be 3 numbers, but its shape is {}",
                         arg.shape
                     )));
                 }
@@ -1377,7 +1377,7 @@ fn layout_text_impl(size: Value, text: Value, env: &mut Uiua) -> UiuaResult<Valu
                     [h, w] => [h, w],
                     _ => {
                         return Err(env.error(format!(
-                            "Size must be a scalar or list of 2 numbers, but it's shape is {}",
+                            "Size must be a scalar or list of 2 numbers, but its shape is {}",
                             arg.shape
                         )))
                     }
@@ -1412,7 +1412,7 @@ fn layout_text_impl(size: Value, text: Value, env: &mut Uiua) -> UiuaResult<Valu
                     [r, g, b, a] => ([r, g, b], Some(a)),
                     _ => {
                         return Err(env.error(format!(
-                        "Color must be a scalar or list of 3 or 4 numbers, but it's shape is {}",
+                        "Color must be a scalar or list of 3 or 4 numbers, but its shape is {}",
                         arg.shape
                     )))
                     }