fix for PHP warning "is_file(): open_basedir restriction in effect"

Example:
PHP Warning: is_file(): open_basedir restriction in effect. File(/home/users/.../user/plugins/.gitkeep/.gitkeep.yaml) is not within the allowed path(s): (/home/users/.../:/usr/share/pear/) in .../web/system/src/Grav/Common/Config.php:237
assets attributes implemented
PHPDocs updated
Merge pull request #46 from rindeal/feature/configurable-assets-attributes

Feature/configurable assets attributes
reverted back to file-only checks, changed to file_exists()
Merge pull request #47 from rindeal/feature/config-fixes

fix for PHP warning "is_file(): open_basedir restriction in effect"
Revert "reverted back to file-only checks, changed to file_exists()"

This reverts commit d234b8e2128356a5d7c76e7d7048c21a26bd49c2.
final workaround for PHP bug 52065
Merge pull request #48 from rindeal/feature/config-fixes

fix for PHP warning "is_file(): open_basedir restriction in effect", round 2
Fixed use of streams. Using YAML_EXT constant for the extension. Changed get and all methods to static
fixes for themes streams and such
getList was returning nothing
override modified only if a non-markdown file was modified
removed stray test page
Reverted streams for theme
Added barDump() to Debugger
Added shutddown event to flush buffer and set content length (tracy-safe)
removed barDump() test :)
added onShutdown event that fires after the connection has been closed (background processing)
Added an option to disable the shutdown close connection to help with debugging