manual: remove duplicated descriptions from cfunctions

[tueda]

Currently, the properties described in the cfunctions section are incomplete compared to those in the functions section. It would make sense to remove the duplicated descriptions from the cfunctions section and link to functions instead.

This PR also:

• Adds cross-links to nfunctions and ctensors in the functions section.
• Also fixes the following broken text in the PDF:
  

[coveralls]

coverage: 53.352% (-0.003%) from 53.355%
when pulling 714c303 on tueda:pr/docs/remove-cfunctions-properties
into f0423c7 on form-dev:master.