Split HDF5 code from libsrc4 code

[edhartnett]

This has been discussed a lot already, so I will summarize: the goal is to split the HDF5 code from the libsrc4 code. This is to support user-defined formats. The user-defined formats will use the libsrc4 code, but not the HDF5 code.

Fixes #926.
Fixes #856.
Part of #177.

[edhartnett]

The travis failure here was the HDF5 plugin copy problem.

[DennisHeimbigner]

This change will take a lot of time to review. So you will have to wait a bit.
However, this is an important and desirable change.

[edhartnett]

@DennisHeimbigner I tried to make minimum changes to achieve the goal, but there were quite a few.

These changes were suggested by, and helpful to, user-defined formats, but are not actually required. I can also submit the user-defined format changes as a separate PR. However I don't want to overload you guys with changes so I will wait a bit for that.

[edhartnett]

I have brought this PR up to date with master, including merging in changes from PR #934.

[edhartnett]

@DennisHeimbigner any progress on taking a look at this? I would like to get it merged and put up my user-defined formats PR. Thanks.

[edhartnett]

I believe I must take this down and re-do it, in light of all the changes to the code since I submitted it.

@DennisHeimbigner do you have any more libsrc4 changes underway? I would like the next time I re-do this to be the final time, if that's OK.

[DennisHeimbigner]

I can hold off until your mod is completed.
I assume that, for now, the form of the split off fields
of NC_HDF5_FILE_INFO are left as in in the new split off
structure so that at least you do not have to do anything more
than changes some occurrences of NC_HDF5_FILE_INFO
to be the new structure type.

[edhartnett]

@DennisHeimbigner I have retreated from my giant PR and will present these changes in more manageable bites.

In my first PR I move some files and create the new libhdf5 directory. in the next PR I will add all the other new files needed, and move some functions around.

Once those changes are merged, the rest of the changes will be much less sensitive to others making changes on the code. When a function is moved to a new file in another directory, git loses all track of it.

Thanks!