Add pear modules, mail and net_smtp via composer (#93)

Add pear modules, mail and net_smtp via composer, remove php 5.6 build due to phpunit 6

lib/composer/vendor/symfony/yaml/Tests/Fixtures/numericMappingKeys.yml

@@ -0,0 +1,23 @@
+--- %YAML:1.0
+test: A sequence with an unordered array
+brief: >
+  A sequence with an unordered array
+yaml: |
+  1: foo
+  0: bar
+php: |
+  array(1 => 'foo', 0 => 'bar')
+---
+test: Integers as Map Keys
+brief: >
+    An integer can be used as dictionary key.
+yaml: |
+    1: one
+    2: two
+    3: three
+php: |
+    array(
+        1 => 'one',
+        2 => 'two',
+        3 => 'three'
+    )