v0.2.16-pre.2

fix: stop filtering cvflann typedefs out of evision_generated_enums.h

PR #312 added a HAND_WRITTEN_ENUM_CONVERTERS filter that suppressed
gen_enum_reg for cvflann_flann_algorithm_t and cvflann_flann_distance_t
to avoid colliding with hand-written evision_to/evision_from converters
in evision_custom_headers/evision_flann.hpp. Commit 09c5cbd had already
removed those hand-written converters (now emitted by gen2 after the
defines.h parsing fix), so the filter now suppresses *both* the
converters and, critically, the typedef -- and evision_generated_types_content.h
still references cvflann_flann_distance_t in the cv::flann::Index
constructor, leaving the NIF build with 'cvflann_flann_distance_t was
not declared in this scope' errors.

Drop the filter so gen_enum_reg emits the typedef + CV_ERL_FROM_ENUM +
CV_ERL_TO_ENUM unconditionally for these types, matching every other
enum.

Verified locally: regenerated headers contain all four cvflann typedefs,
evision.so rebuilds without errors, all 5 tests in
test/evision_flann_test.exs pass.