Suggested changes for sections: energy demand & tech change

[Jihoon]

Minor edits and improvements

In technological change section, it would be helpful to add remarks on how general diffusion constraints are determined for different technologies or what the values are based on.

[Jihoon]

For 'Energy demand':

• Clarified the key assumption under the quantile regression etc. (as far as I understand it.)
• The explanation about the regressions was extremely difficult to read. I separated out the dependent variables for the regional regression as bullets.
• 'the user' -> 'users'
• Removed the uses of 'several'
• "Several user-defined inputs allow..." & "Given these input parameters, ..." <- By carefully reading it, I guess these inputs indicate the convergence quantile and income. I added them in the text.
• Table captions indicate the dependent variables (FEI, shares, etc.) as 'parameter', which generates confusion with the 'input parameters' in the text. Changed to 'variable'

[jkikstra]

@Jihoon I was assigned to check up on this PR. A few comments:

I very much like the textual changes in the documentation, it is much clearer now.

Things that should be changed:

1. I believe that these changes should first be committed to #20 (https://github.com/iiasa/message_doc/tree/2019-update) rather than directly to the master.

Minor textual points that could be considered:

2. Rather write "quantity" than "variable", to be fully generic in the description of the tables.

3. A space is missing after *t* for t=0 at the line "Fig. 13 below illustrates the maximum technology growth starting at a level of 1 in year t=0 for ... "

As there is no-one besides yourself assigned to review these changes (see assigned reviewers), it's up to you to decide whether someone else should still look at this before committing to the 2019-update (#20) branch.

[Jihoon]

replaced with #34