Remove an extra "for"
Update Documenting-functions.rmd

Removed a line about the `@genericMethods` tag, which is not implemented in roxygen2.
sorry if the omission was intentional
case sensitive
Fixed typo
Update Functionals.rmd
fixed typo at line 730, from 'solve' to 'solving'
Update Data-structures.rmd

Fixed typo.
Proof reading chapter 9
Index for chapter 9
Proof reading chapter 10
Index for chapter 10
Index improvements and standardisation
Fix case
Proof reading chapter 11
Index for chapter 11
Proof reading chapter 12
Index for chapter 12
Proof reading chapter 13
Index for chapter 13