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/yum/README.md

@@ -1,28 +1,25 @@
-Yum
-===
+# Yum
 
-Defines [yum][1] aliases.
+Defines [*yum*][1] aliases.
 
-Aliases
--------
+## Aliases
 
-  - `yumc` removes package(s) and leaves.
-  - `yumi` installs package(s).
-  - `yumh` displays history.
-  - `yuml` lists packages.
-  - `yumL` lists installed packages.
-  - `yumq` displays package information.
-  - `yumr` removes package(s).
-  - `yums` searches for a package.
-  - `yumu` updates packages.
-  - `yumU` upgrades packages.
+- `yumc` removes package(s) and leaves.
+- `yumi` installs package(s).
+- `yumh` displays history.
+- `yuml` lists packages.
+- `yumL` lists installed packages.
+- `yumq` displays package information.
+- `yumr` removes package(s).
+- `yums` searches for a package.
+- `yumu` updates packages.
+- `yumU` upgrades packages.
 
-Authors
--------
+## Authors
 
 *The authors of this module should be contacted via the [issue tracker][2].*
 
-  - [Sorin Ionescu](https://github.com/sorin-ionescu)
+- [Sorin Ionescu](https://github.com/sorin-ionescu)
 
 [1]: http://yum.baseurl.org
 [2]: https://github.com/sorin-ionescu/prezto/issues