add glpk-hs package

it references sci-mathematics/glpk

tested against glpk-4.48 and this sample script:
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import           Control.Monad.LPMonad
import           Data.LinearProgram
import           Data.LinearProgram.GLPK

objFun :: LinFunc String Int
objFun = linCombination [(10, "x1"), (6, "x2"), (4, "x3")]

lp :: LP String Int
lp = execLPM $ do
    setDirection Max
    setObjective objFun
    leqTo (varSum ["x1", "x2", "x3"]) 100
    leqTo (linCombination [(10, "x1"), (4, "x2"), (5, "x3")]) 600
    leqTo (linCombination [(2, "x1"), (2, "x2"), (6, "x3")]) 300
    varGeq "x1" 0
    varBds "x2" 0 50
    varGeq "x3" 0
    setVarKind "x1" IntVar
    setVarKind "x2" ContVar

main = print =<< glpSolveVars mipDefaults lp
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