Rename files for consistency

[eddyashton]

Resolves #707.

We have no fixed naming scheme for our file names. This PR adds one - we snake_case.h the basenames (dirs are still namespacelikeconcatenated dirs are also now ./snake_case/snake_case.h).

Opening as a draft so people have a chance to veto if they wish, but I'd like to clear this tonight/tomorrow morning so I don't spend too much time resolving conflicts.

Do we like this style?
Do we prefer oneword for some of our core concepts? eg this PR says ring_buffer.h, key_pair.h, etc, does this go too far?
I've ignored libbyz/ so far - should I lower-case those files in the same PR? This now also renames libbyz files to lower_snake_case. This reordered some includes in breaking ways, so there are additional include statements to correct this.

[achamayou]

+1 for this convention. Can we have a quick script that checks all source files match that convention? [a-z_]+?

[olgavrou]

I like this style, I prefer ring_buffer vs ringbuffer just so that it is consistent throughout. If you want to also do libbyz then go for it, but it can comfortably go into a different PR (might be quicker to merge this without libbyz at this point)

[achamayou]

@eddyashton I suggest we align directories also, at least things like: /src/apps/jsgeneric/js_generic.cpp, as well as public headers, and probably binary artifacts too (js_generic.enclave.so.signed)?

[jumaffre]

LGTM.

[eddyashton]

check-format.sh now checks that filenames are lower_snake_cased. It can't check you've put underscores in sensible places, we'll have to enforce that manually. I've also converted libbyz, rather than adding an exception to it for this check.

[achamayou]

@eddyashton thank you for taking the time to do this, the repo looks much cleaner now!

[codecov-io]

Codecov Report

Merging #989 into master will increase coverage by 4.43%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #989      +/-   ##
==========================================
+ Coverage   63.19%   67.63%   +4.43%     
==========================================
  Files         135      103      -32     
  Lines        8971     8266     -705     
==========================================
- Hits         5669     5590      -79     
+ Misses       3302     2676     -626     

Flag	Coverage Δ
#unit_BFT	?
#unit_CFT	67.63% <ø> (?)

Impacted Files	Coverage Δ
src/apps/lua_generic/lua_generic.cpp	75.28% <ø> (ø)
src/consensus/ledger_enclave.h	44.44% <ø> (ø)
src/consensus/pbft/pbft_requests.h	0.00% <ø> (ø)
src/consensus/raft/raft.h	76.23% <ø> (ø)
src/consensus/raft/raft_types.h	91.67% <ø> (ø)
src/crypto/crypto_box.h	80.00% <ø> (ø)
src/crypto/symmetric_key.cpp	86.54% <ø> (ø)
src/crypto/symmetric_key.h	54.84% <ø> (ø)
src/ds/champ_map.h	92.54% <ø> (ø)
src/ds/logger.h	49.73% <ø> (ø)
... and 64 more

[ghost]

file_snake_casing@6436 aka 20200325.32 vs master ewma over 30 builds from 6062 to 6428