saugns v0.3.10b. Various fixes. Add freqlinkPM syntax.

Fixes:
 * Audio: The v0.3.9 oscillator produced jagged shapes
   and audible distortion when PM modulator amplitudes
   were large. Fixed but made generation a bit slower.
 * Numerical expressions: Fixed parsing of unary minus
   several times in a row and in combination with "^".
 * Timing syntax: Correct handling of "\" after ";" in
   compound steps for modulator operators. Re-set time
   using the last default value, not the last explicit
   "t" value. Makes implicit time handling consistent.

Syntax changes:
 * Add new "p+f[...]" syntax, for frequency-linked PM.
   Multiplies the amplitude of modulators with carrier
   frequency scaled so that 632.45... Hz has 1.0 gain.
   Based on an idea I remember from 2011, before I got
   normal modulation in order, now seeming worthwhile.

Rework some scripts to show the use of the new syntax.

Clarify documentation a little bit more, regarding FM.
This tag has no release notes.