Noted limitations in OpenMM energy output

Fixes #758

Change-Id: I1520fc3b1b9ac4707468b580953642d9ffd1b64e
Fixed incorrect statement about RB dihedrals.

Fixed bug in manual stating that RB dihedrals can not be combined
with 1-4 interactions.

Change-Id: I3c31eedcd34aef5b2a5bf0baf0d5ec3c75479b26
Update to 4.5.6 version

Change-Id: I960b73c9efb0fad3f9aa709cd89835b3f7922cc3
Fixed unit for Urey-Bradley angle force constant.

Change-Id: Ifeb669296a560685422e141415999378eac8ab37
Merge branch 'release-4-5-patches' into release-4-6

Conflicts:
	CMakeLists.txt
	special.tex
	topology.tex

Change-Id: I6e36a6d6322fef00f5e9114f1fb51950f90f472a