Removed pyramid section and unused material.

with explanation of expm1; compatible polyhedron section.

Wuttke, Joachim authored 9 years ago and Wuttke, Joachim committed 9 years ago

Nicer derivation, wrong handling of const term,
wrong handling of singularity.

based on contour integral, without apparent singularities.
Validated against old (Rémy/Céline) implementation: agrees,
except for strong deviations near q->0, where the new
implementation is smoother.
The analytical calculations are explained in App. C2 of the manual.
This resolves #1300.

Manual: polygon by line integral.