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/legacyBooleanMappingKeys.yml

@@ -0,0 +1,23 @@
+--- %YAML:1.0
+test: Miscellaneous
+spec: 2.21
+yaml: |
+  true: true
+  false: false
+php: |
+  array(
+    1 => true,
+    0 => false,
+  )
+---
+test: Boolean
+yaml: |
+   false: used as key
+   logical:  true
+   answer: false
+php: |
+   array(
+     false => 'used as key',
+     'logical' => true,
+     'answer' => false
+   )