Add PTC and 0-20mA documentation
Merge branch 'master' of github.com:Tinkerforge/doc

Conflicts:
	de/source/Hardware/Bricklets/Industrial_Dual_0_20_mA.rst
	en/source/Hardware/Bricklets/Industrial_Dual_0_20_mA.rst
Add finished (bar images) dual 0-20ma and ptc bricklet documentation (not yet in index)