v0.5.16

ApproxFunBase v0.5.16

Diff since v0.5.15

Merged pull requests:

• Move show methods from ApproxFun (#122) (@jishnub)
• fix show for QuotientSpace (#123) (@jishnub)
• Type stability in promote spaces (#124) (@jishnub)
• backport type stability in promote spaces (#125) (@jishnub)