Installation issues under Linux due to vamp

[hagenw]

As mentioned already in #26 the straightforward installation with pip can fail due to vamp.

I got under Ubuntu 18.04 using Python 3.6.9:

$ pip install omnizart
...
ERROR: Cannot install omnizart==0.1.0, omnizart==0.1.1, omnizart==0.2.0, omnizart==0.3.0, omnizart==0.3.1, omnizart==0.3.2, omnizart==0.3.3, omnizart==0.3.4, omnizart==0.4.0 and omnizart==0.4.1 because these package versions have conflicting dependencies.

Installing numpy manually first as proposed in #26 does indeed solve this issue. I'm not completely sure if this can be solved by putting numpy as a direct dependency to setup.py as proposed in #26, but maybe you can try. Otherwise please expand the installation instructions accordingly.

[BreezeWhite]

I've tried to explicitly put numpy as the dependency, but seems not work. I've updated the documentation to inform users to install numpy and Cython before installing omnizart.

[keunwoochoi]

(Commenting to link this to openjournals/joss-reviews#3391)

[hagenw]

Thanks.