add: direct support for float values
add: direct support for float and int values
chg: refactoring of integer and float handling
CHG: cs:float mapped to BigDecimal in order to keep information about
scale and precission
add: introduced explicit subclasses for feature-value-types
chg: adjusted to support explicit sub-types of feature-values
del: removed footer
fix: level of concepts
add: optional scale and rounding for float-values
add: optional scale and rounding for float-feature-values
fix: mathematical operations on datalayer not interface objects!