Unified Code for Units of Measure (UCUM) implementation for FHIR.

UcumReader now reads UCM essence xml set. And parses basic conversions and more Complex conversions Example:

Quantity q = system.Convert("4.3[psi]'");

will result in

{[2,25 ± 0,005649]E2 g.m-1.s-2} (approximated)

Classes:

• Exponential (Normalized Scientific Notation number, with error propagation)
• Unit (measurable dimensions like gram, meter, Kelvin, pound force, etc.)
• Prefix (kilo, mega, mili, micro etc.)
• Metric (A composite set of (prefixed) units like m/s, kg.m/s2)
• Quantity (a measurement: Exponential + Metric)
• UcumReader (reader of the XML essence of UCUM)

TODO:

• UcumReader doesn't implement special cases (like fahrenheid/celcius conversion formulas)
• Add support for nested terms