small bug fix
Fixed overwriting of multiple annotations for the same item in analogsignals and spiketrains
changed pynn uS from 1e-9*S to 10e-6*S
changed pynn uS from 10e-6*S to 1e-6*S
Merge pull request #20 from dguarino/master

 changed pynnio uS from 1e-9*S to 1e-6*S