src/template/base.php: Implement support for rendering template stored in file (on local filesystem).
src/: Remove functions related to "reflection" to reflection.php, under \SpareParts\Reflection namespace; add 'numberOfParameters' method to this module; and update all other references to reflection-related functions.
src/webapp/forms.php: Allow for two types of validation functions for Field objects, those that accept only one parameter (the simple string value to validate) and those that accept two parameters (the field object itself, followed by the same simple string value).
src/webapp/forms.php: Explicitly specify abstract methods, 'setValue' and 'renderInputHtml', for class Field; fix some spelling, plus other minor tidying.