re: https://github.com/Unidata/netcdf-c/issues/1642
Modify ncdump, nccopy, and ncgen to support the NC_COMPACT storage option.
Added test cases and added description to the man pages for the utilities.
1. ncdump: For compact storage variable, print special attribute __Storage_ as
````
<var>: _Storage = "compact";
````
2. ncgen: parse and implement
````
<var>: _Storage = "compact";
````
in a .cdl file
3. nccopy: Extend the chunk specification (-c flag) to support
compact using the forms
````
nccopy ... -c <var>:compact
and
nccopy ... -c <var>:contiguous
````
Misc. other changes
1. cleanup the copy_chunking function in ncdump/nccopy.c
The code for handling character constants
in datalists in ncgen has some problems.
1. It failed on large constants
2. It did not handle e.g. var = 'a', 'b', ...
in the same way that ncgen3 did.
3. The code for generate.c and genchar.c needed
some refactoring to make it a little simpler
(but not simple).
