Unimplemented features moved to their own exception (#1361)

Unimplemented features moved to their own exception

InternalCompilerError is an exception that really should be reserved for
actual internal errors of the compiler.  Unimplemented features can now
use either solUnimplemented( ) or, if it should be conditional, then
solUnimplementedAssert( ).

* Revert some unimplemented exceptions, add handlers

The jsonCompiler and CommandLineInterface needed handlers for the
new UnimplementedFeatureException, and some cases I had moved on to
the new exception were better treated as real internal compiler
errors.

* Standardize on "Unimplemented feature" message

libsolidity/codegen/ArrayUtils.cpp

@@ -270,7 +270,7 @@ void ArrayUtils::copyArrayToStorage(ArrayType const& _targetType, ArrayType cons
 
 void ArrayUtils::copyArrayToMemory(ArrayType const& _sourceType, bool _padToWordBoundaries) const
 {
-	solAssert(
+	solUnimplementedAssert(
 		!_sourceType.baseType()->isDynamicallySized(),
 		"Nested dynamic arrays not implemented here."
 	);