Added build files to turn the bible into a book

manuscript/chapter12.txt

@@ -1,13 +1,51 @@
-# Performance
+# Obsolete Syntax
 
-## Disable Unicode
+## Shebang
 
-If your script doesn't require unicode, you can disable it for a speed boost. Results may vary but I've seen an improvement in Neofetch and some other smaller programs.
+Use `#!/usr/bin/env bash` instead of `#!/bin/bash`.
+
+- The former searches the user's `PATH` to find the `bash` binary.
+- The latter assumes it is always installed to `/bin/` which can cause issues.
 
 ```shell
-# Disable unicode.
-LC_ALL=C
-LANG=C
+# Right:
+
+    #!/usr/bin/env bash
+
+# Wrong:
+
+    #!/bin/bash
+```
+
+## Command Substitution
+
+Use `$()` instead of `` ` ` ``.
+
+```shell
+# Right.
+var="$(command)"
+
+# Wrong.
+var=`command`
+
+# $() can easily be nested whereas `` cannot.
+var="$(command "$(command)")"
+```
+
+## Function Declaration
+
+Don't use the `function` keyword, it reduces compatibility with older versions of `bash`.
+
+```shell
+# Right.
+do_something() {
+    # ...
+}
+
+# Wrong.
+function do_something() {
+    # ...
+}
 ```
 
 <!-- CHAPTER END -->