general: Reformat documentation with better formatting and wording

General purpose reformating and rewording in (a few places). This should
also make markdown linting happier.

Prefer back-ticks wherever useful and use `console` for code blocks to
be executed on terminal.

Also, update references links wherever possible (including update from
'http://' to 'https://').

modules/gnu-utility/README.md

@@ -1,9 +1,8 @@
-GNU Utility
-===========
+# GNU Utility
 
 Provides for the interactive use of GNU utilities on BSD systems.
 
-Installing GNU utilities on non-GNU systems in `$PATH` without a prefix, i.e.
+Installing GNU utilities on non-GNU systems in `$PATH` without a prefix, i.e.,
 `ls` instead of `gls`, is not recommended since scripts that target other
 utilities will be broken.
 
@@ -12,23 +11,21 @@ use.
 
 This module must be loaded **before** the *utility* module.
 
-Settings
---------
+## Settings
 
 ### Prefix
 
-To use a different prefix, add the following to *zpreztorc*, and replace 'g' with
-the desired prefix:
+To use a different prefix, add the following to *~/.zpreztorc*, and replace 'g'
+with the desired prefix:
 
 ```sh
 zstyle ':prezto:module:gnu-utility' prefix 'g'
 ```
 
-Authors
--------
+## Authors
 
 *The authors of this module should be contacted via the [issue tracker][1].*
 
-  - [Sorin Ionescu](https://github.com/sorin-ionescu)
+- [Sorin Ionescu](https://github.com/sorin-ionescu)
 
 [1]: https://github.com/sorin-ionescu/prezto/issues