Document public interface of cfs_tpfa_residual module

This is Doxygen-style reference documentation only.
Merge branch 'master' into gravity-in-wells
Document public interface of compr_quant_general module

This is Doxygen-style reference documentation only.
Reformat to add Doxygen markup where appropriate
Document public interface of compr_source module.

This is Doxygen-style reference documentation only.
Rename CompletionData::gpot -> wdp .

This is in preparation of implementing actual gravity support in
(compressible) well-pressure solution.
Update documentation accompanying CompletionData structure.

Specifically, the 'wdp' member is a scalar value at each well
connection.  Phase behaviour is incorporated through other means.
Don't compare floating point numbers for equality.
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells
Merge branch 'master' into gravity-in-wells