C++ example: read last line even with no final newline.
Add api functions to change the frame size and reload fonts.

These are currently untested.
Aegisub example: improve behavior.

This commit updates the API usage to pass the header/body string
lengths. It also adds methods corresponding to the new API functions
for updating the resolution and reloading the fonts.

Additionally, fonts are now reloaded every run, even if the
ASSInspector library has already been initialized.