Introduced OFnumeric_limits.

The template OFnumeric_limits provides a standardized way to query various
properties of fundamental types (e.g. the largest possible value for type
int is OFnumeric_limits<int>::max()).
OFnumeric_limits is compatible to C++11's std::numeric_limits.
Documented DCMTK's C++ cast macros.

It is noted in particular that OFdynamic_cast should not be used in DCMTK.
Fixed typo in comment.
Added new temporarily generates files.