Remove `B` pitch bend operation (altered by `B=`), `P`, `E`, `V`, ... too

[atsushieno]

Pitchbend operation B can bring in syntactical confusion in combination with B-, because we may perform pitch bend changes like:

• B -100 i.e. set absolute B value to -100 (which is 8192 - (100 * bend_cent_mode_intermadiate))
• B- 100 i.e. set relative B value by -100 (which is current_pitch_bend - 100 * bend_cent_mode_intermadiate)

and if we write B-100 to set absolute value, we find it not working and get lost. B- takes precedence by because our tokenizer finds B- as the longest match.

A better syntax would be to change B as relative operation, but immediately making it so would make old MMLs inaccurate.

Therefore we set B= as the new absolute pitchbend operation, and remove B from the next major upgrade (mugene-ng 2.0?).

[atsushieno]

To be clear, it was not only about pitchbend. Various MML operations such as E, V, P, M, t, etc. all with relative specifiers had the same issue.