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
Files that have many tracks, each with tempo information
were near impossible to load (30+ mins on modern 4.2Ghz CPU!),
because tempo is parsed incrementally:
```
For each new track:
for each new tempo-event:
rewind()
for each loaded track so far:
for each event on this track so far
```
This reduces the complexity from O(tracks^2 * tempos^2)
to O(tracks * tempos).
"Come Thou Fount Tempo Map.mid" has 238 Tracks and 56168 total
Tempo Changes (236 per track). This now requires only 56168 iterations
in smf_create_tempo_map_and_compute_seconds, rather than 1.64e+9
iterations
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.
