Markdown formatting fixes

- mark all code blocks with ```
- unify empty lines between sections
- adjust list syntax (no space before dash)
- adjust headers to use Atx-style syntax
- remove trailing spaces

developer/code/source-code.md

@@ -14,11 +14,11 @@ Qubes Source Code Repositories
 All the Qubes code is kept in Git repositories. We have divided the project into
 several components, each of which has its own separate repository, for example:
 
- * `core-admin.git` -- The core Qubes infrastructure, responsible for VM
+* `core-admin.git` -- The core Qubes infrastructure, responsible for VM
    management, VM templates, fs sharing, etc.
- * `gui-daemon.git` -- GUI virtualization, Dom0 side.
- * `gui-agent-linux.git` -- GUI virtualization, Linux VM side.
- * `linux-template-builder.git` -- Scripts and other files used to create Qubes
+* `gui-daemon.git` -- GUI virtualization, Dom0 side.
+* `gui-agent-linux.git` -- GUI virtualization, Linux VM side.
+* `linux-template-builder.git` -- Scripts and other files used to create Qubes
    template images.
 
 All of our repositories are available under the [QubesOS GitHub account].
@@ -35,9 +35,9 @@ e.g.:
 git clone https://github.com/QubesOS/qubes-core-admin.git core-admin
 ~~~
 
-To build Qubes you do not need to download all these repositories.  
+To build Qubes you do not need to download all these repositories.
 If you use [qubes builder] you can specify *what* you want to build, and download only the repositories needed to build that target.
- 
+
 If you really do want to clone **all** of the repositories, you can use these commands:
 
 ~~~
@@ -53,21 +53,20 @@ find . -mindepth 1 -maxdepth 1 -type d -exec git -C {} fetch --tags --recurse-su
 
 (Alternatively, you can pull instead of just fetching.)
 
-
 How to Send Patches
 -------------------
 
 If you want to [contribute code] to the project, there are two ways. Whichever
 method you choose, you must [sign your code] before it can be accepted.
 
-*  **Preferred**: Use GitHub's [fork & pull requests].
+* **Preferred**: Use GitHub's [fork & pull requests].
 
    Opening a pull request on GitHub greatly eases the code review and tracking
    process. In addition, especially for bigger changes, it's a good idea to send
    a message to the [qubes-devel mailing list] in order to notify people who
    do not receive GitHub notifications.
 
-*  Send a patch to the [qubes-devel mailing list] (`git format-patch`).
+* Send a patch to the [qubes-devel mailing list] (`git format-patch`).
 
    1. Make all the changes in your working directory, i.e. edit files, move them
       around (you can use 'git mv' for this), etc.