This would realloc a buffer for every event, making it absurdly slow for
large MIDI files (say, 10k events). Use the somewhat standard heuristic
of doubling the requested allocation every time we need to increase the size.
This results in a speedup of 40-100x when saving SMF to disk
This significantly speeds up parsing MIDI files with complex
tempo-maps. e.g. "Black MIDI Trilogy_2.mid" has 24134 Tempo
changes. Prior to this commit parsing that file took over 5 minutes.
now it loads in under one seconds (libsmf only; libardour still
add overhead, and now needs about 30-40 seconds, previously
it took about 10 mins).
The problem was that every call to `smf_track_add_event_pulses()`
calls `seconds_from_pulses()` which calls `smf_get_tempo_by_seconds()`
which iterates over the tempo-map:
for every midi-event { for ever tempo until that midi-event {..} }
This does not scale to 3.5M events and 24k tempo-changes.
