Forestclaw2d.h vs. convenience

[cburstedde]

1. Going through forestclaw2d.h and fclaw2d_convenience.h, I'm thinking it may be reasononable to move

• fclaw2d_domain_destroy
• fclaw2d_domain_adapt
• fclaw2d_domain_partition*
• fclaw2d_domain_complete

into forestclaw2d.h. This will allow us to remove the inclusion of fclaw2d_convenience.h. from most forestclaw files.

2. Recently @scottaiton proposed to remove obsolete functions from these files. We'd be grateful for a list to clean them up.

Any comments?