- Commented several empty sections in mkdocs.yml (will reactivate them later if someone fills them)

- Enabled 'Directory Structure' section that was not present in mkdocs.yml
- Removed all links to empty sections
- Fixed incorrect links that led to a 404 error
- Updated art covers url
- Redirected former FunKey OS links to my release page
- Updated a few things in some sections
- Fixed a few typos

docs/developer_guide/software_reference/boot_process/index.md

@@ -39,15 +39,15 @@ order:
 
  - The [SPL][3] (Secondary Program Loader)
 
- - The [U-Boot bootloader][4]
+ - The U-Boot bootloader
 
- - The [Linux kernel][5]
+ - The Linux kernel
 
- - The userland [System V init scripts][6]
+ - The userland System V init scripts
 
 ## Shutdown Process
 
-Unlike the startup process, the [shutdown process][7] is much more
+Unlike the startup process, the shutdown process is much more
 straightforward, but it must be optimized to run as quiclky as
 possible, as the time from when the shutdown is initiated when the
 user press the <i class="funkey-menu"></i> key or close the **FunKey