New Directive::__construct
SrcDirective::setValue enforces SourceList value with InvalidArgumentException
Improve coverage reports with coversNothing
Unit tests for Direcetive and SrcDirective
Correct check for argument type
Move Token and TokenList under Util namespace
Add more directive tests
Add test for CSP header class
Add test for Util\Token
Process uncovered files for code coverage
Put namespace on same line as opening PHP tag
Remove underscore prefix from properties

Previously private and protected properties used an underscore
prefix.
Put class brace on the next line
Use camelCase in properties names
Put comma after each multi-line array element
Prefix abstract clases with "Abstract"
Suffix intefaces with "Interface"
Put control structures opening brace on same line
Use PSR-4 autoloader

It allows for less directory nesting
Add composer selfupdate to Travis CI script

Also use `before_install` and `install` phases instead of `before_script`.