Outdated 'dimensions' formalism in some parts of the docs

[FLomb]

Description

Some parts of the docs, e.g. the Math syntax, still suggest using dimensions as a string to specify dimensions for parameters of other pieces of math in the yaml files.

This is, however, outdated. The latest formalism is dims.

Related links

• https://calliope.readthedocs.io/en/v0.7.0.dev3/user_defined_math/syntax/

Version

0.7.0dev3

Proposed change

Systematically search through the docs to find and replace dimensionos: with dims: in code snippets.