Merge pull request #6 from tristanlins/master

Add support for "symlinks", "userfiles" and "runonce" sections.
Merge pull request #7 from tristanlins/master

Fix "$contao is not an array" when { extra: contao: {} } not set
Merge pull request #8 from tristanlins/master

Fix issue with links that have an invalid target
Merge pull request #9 from tristanlins/master

Fix outdated composer module path
Fix problems destroying the composer.json

The regexp replacement of the contao version sometimes destroy the
composer.json. Now it is using the class JsonFile that should work
better.
Prevent direct access to static::$runonces while generating runonce executor.
Mark installer supports legacy-contao-module packages.
Add support for legacy modules and shadow copies.
Make contao root dir configurable with { extras: { contao: { root: "relative path to root" } } }.
Reformat code.
Create parent directories for symlink.
Remove usage of constant TL_ROOT.
Load constants.php and localconfig.php while search contao root path.
Use getContaoRoot() where needed instead of "..".
Fix illegal access to $this in static context.
Load default.php instead of config.php on Contao 3.
Check if contao core is within vendor/contao/core, if so, use it from there.
Merge pull request #10 from discordier/master

Make the installer recognize the contao core within vendor