Fix horizontal scaling issue in CHEBFUN/ROOTS.
Fixing bugs in sum@unbndfun and isdecay@chebtech for handling array-valued functions.

A few tests are added.
Merge remote-tracking branch 'upstream/development' into fix-unbndfun-sum
A few minor fixes which are missed from the previous push. An additional test is added.
Merge branch 'development' into fix-unbndfun-sum
Merge pull request #931 from chebfun/fix-chebfun-roots

Fix horizontal scaling issue in CHEBFUN/ROOTS.
Merge remote-tracking branch 'chebfun/development' into fix-prefs
Reorganise DOCs.
Add comment about case.
Add a comment about how V4 syntax relates to V5.