Bug: 1-port Z_to_S gives error about matrix shape

This commit fixes the bug in the title. The fix is simple and involves
checking if the matrix is 1-dimensional and taking the required action
if it is.
Merge branch 'master' of https://github.com/seilis/microwave
Smith Chart

Fixed a bug where the horizontal axis (real line) would extend beyond
the Smith chart. This was fixed by changing the addition of an axis line
to the addition of an arbitrary line between (-1,1) at y=0.