Update linalg.rst

Updated the documentation for `Base.LinAlg.BLAS.gemv!` based on:

http://www.math.utah.edu/software/lapack/lapack-blas/dgemv.html
Merge pull request #8510 from krislock/patch-1

Update linalg.rst
allow fully-evaluated keyword argument pairs. closes #7704

anything in an argument list after a ; that's not of the form `a=b` will
be evaluated and expected to be some kind of pair of a symbol and value.
Merge branch 'master' of github.com:JuliaLang/julia into jb/dictsyntax