[#989]: Update monolog requirement to 1.6

phpDocumentor now uses the ErrorHandler of Monolog but that wasn't available
until 1.6. Given that the composer.json is locked on 1.4 we need to bump the
requirement to 1.6.
Merge pull request #991 from mvriel/989

[#989]: Update monolog requirement to 1.6
Add shebang for Phar file to enable +x
Fix absence of FileDescriptor checking
Cleaned up unused code
[#985]: Fix missing namespaces and classes folder and contents
[#985]: fix erroneous paths
Update CHANGELOG for recent changes
Update dependencies to pull in a new template version
Merge branch 'master' of github.com:phpDocumentor/phpDocumentor2
Update lock file to new asset installer