add symengine to stackage
add symengine to stackage

Add symEngine haskell bindings (https://github.com/symengine/symengine.hs)
jaspervdj/stackage,fimad/stackage,alanz/stackage,jonschoning/stackage,DanielG/stackage,judah/stackage,spencerjanssen/stackage,k0ral/stackage,soenkehahn/stackage,lwm/stackage,creichert/stackage,asr/stackage,stackbuilders/stackage,phaazon/stackage,codedmart/stackage,Shimuuar/stackage,GregorySchwartz/stackage,wereHamster/stackage,garetxe/stackage,peti/stackage,ygale/stackage,iand675/stackage,mstksg/stackage,brendanhay/stackage,simonmichael/stackage,mgajda/stackage,athanclark/stackage,christiaanb/stackage,ethercrow/stackage,mrkkrp/stackage,massysett/stackage,l29ah/stackage,fpco/stackage,clinty/stackage,michalkonecny/stackage,Daniel-Diaz/stackage,int-index/stackage,phadej/stackage