documentation cleanup

 * In preparation of #930 work
 * Remove/reorder duplicate documentation from Makefile/Unit-tests.md/Download-and-Installation.md (composer information is now in Unit-tests.md)
 * Installation using git: add composer requirement to all git installation procedures, add python3-virtualenv requirement
 * Styling (horizontal rulers, spacing, descriptive headers)

1 files changed, 6 insertions, 4 deletions

diff --git a/doc/md/Unit-tests.md b/doc/md/Unit-tests.md
index d200634f..f6030d5c 100644
--- a/doc/md/Unit-tests.md
+++ b/doc/md/Unit-tests.md
@@ -2,12 +2,12 @@
 
 The framework used is [PHPUnit](https://phpunit.de/); it can be installed with [Composer](https://getcomposer.org/), which is a dependency management tool.
 
-Regarding Composer, you can either use:
+### Install composer
 
-- a system-wide version, e.g. installed through your distro's package manager
-- a local version, downloadable [here](https://getcomposer.org/download/)
+You can either use:
 
-#### Sample usage
+- a system-wide version, e.g. installed through your distro's package manager
+- a local version, downloadable [here](https://getcomposer.org/download/).
 
 ```bash
 # system-wide version
@@ -29,6 +29,8 @@ $ composer update
 
 #### Install and enable Xdebug to generate PHPUnit coverage reports
 
+See http://xdebug.org/docs/install
+
 For Debian-based distros:
 ```bash
 $ aptitude install php5-xdebug