Remarks about EMGM

This is not a pull request. This is a question sheet formulated in the diffs. These are the questions.

1. Is it possible to have implicit values of type `RView` and use them?

2. Section 1.5 of Oliveira, Hinze & Loeh is about a more extensible version of EMGM using multi-parameter type classes. Since scala supports multi-parameter type classes out of the box, would it not be better to investigate the more extensible version? (see `trait EMGM_sec_1_5`)

3. Does EMGM solve the expression problem?