Motivation for this change

This PR gives the structure of a lmdotype R to:

• {linear E -> F} when E, F : lmodType R
• {linear_continuous E -> F} when E F : convextvsType R. It also defined the {linear_continuous _ -> _} structure.

This development is essential to the study of topological duals E' in topological vector spaces, and more generally to the study of closed categories in functional analysis.
Another pull request will enforce the topological structures on {linear_continuous E -> F} ( as a convextvsType, or metric/normed when F is metric or normed).

Checklist

• added corresponding entries in CHANGELOG_UNRELEASED.md

• added corresponding documentation in the headers

Reference: How to document

Merge policy

As a rule of thumb:

• PRs with several commits that make sense individually and that
  all compile are preferentially merged into master.
• PRs with disorganized commits are very likely to be squash-rebased.

Reminder to reviewers

• Read this Checklist
• Put a milestone if possible
• Check labels