Preliminary delivery of blockmesh

[pbtoast]

This adds a few major features to polymec:

1. Blockmesh, a parallel block-structured mesh class that uses unimesh objects for blocks.
2. Blob_exchanger, an exchanger that sends/receives variable-sized binary blobs between processes.
3. Updates, fixes, and cleanup related to field metadata and other niceties.

This hasn't been comprehensively tested, but the basics are there. I'm calling this good enough for now.

Fixes #321

[codecov[bot]]

Codecov Report

Merging #356 into master will decrease coverage by 1.95%. The diff coverage is 47.29%.

@@            Coverage Diff             @@
##           master     #356      +/-   ##
==========================================
- Coverage   80.65%   78.69%   -1.96%     
==========================================
  Files         238      247       +9     
  Lines       37778    39823    +2045     
==========================================
+ Hits        30468    31337     +869     
- Misses       7310     8486    +1176

Impacted Files	Coverage Δ
core/exchanger.h	100% <ø> (ø)	:arrow_up:
geometry/unimesh_copy_bc.c	100% <ø> (ø)	:arrow_up:
core/options.c	100% <ø> (ø)	:arrow_up:
core/unordered_set.h	100% <ø> (ø)	:arrow_up:
core/array.h	100% <ø> (ø)	:arrow_up:
geometry/colmesh_field.h	100% <ø> (ø)	:arrow_up:
geometry/unimesh_periodic_bc.c	100% <ø> (ø)	:arrow_up:
geometry/unimesh_remote_bc.c	74.2% <ø> (ø)	:arrow_up:
geometry/colmesh.h	81.81% <ø> (ø)	:arrow_up:
geometry/constant_unimesh_patch_bc.c	100% <ø> (ø)	:arrow_up:
... and 61 more

---

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Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 4553ce3...2dc8369. Read the comment docs.

[codecov[bot]]

Codecov Report

Merging #356 into master will decrease coverage by 1.74%. The diff coverage is 51.56%.

@@            Coverage Diff            @@
##           master    #356      +/-   ##
=========================================
- Coverage   80.65%   78.9%   -1.75%     
=========================================
  Files         238     247       +9     
  Lines       37778   39890    +2112     
=========================================
+ Hits        30468   31475    +1007     
- Misses       7310    8415    +1105

Impacted Files	Coverage Δ
core/exchanger.h	100% <ø> (ø)	:arrow_up:
geometry/unimesh_copy_bc.c	100% <ø> (ø)	:arrow_up:
core/options.c	100% <ø> (ø)	:arrow_up:
core/unordered_set.h	100% <ø> (ø)	:arrow_up:
core/array.h	100% <ø> (ø)	:arrow_up:
geometry/colmesh_field.h	100% <ø> (ø)	:arrow_up:
geometry/unimesh_periodic_bc.c	100% <ø> (ø)	:arrow_up:
geometry/unimesh_remote_bc.c	74.2% <ø> (ø)	:arrow_up:
geometry/colmesh.h	81.81% <ø> (ø)	:arrow_up:
geometry/constant_unimesh_patch_bc.c	100% <ø> (ø)	:arrow_up:
... and 61 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 4553ce3...2dc8369. Read the comment docs.