Improve compile time

[pmconrad]

Fixes #1738 (hopefully)

The idea is to explicitly specialize certain templates (mostly exceptions, APIs and serialization) in .cpp files and declare them extern in .hpp files. This avoids them being instantiated (and thus compiled) separately whereever they are used.

The result is almost 40% faster build with a significant reduction of required RAM and diskspace. The effect on replay time seems to be lower than the error from measuring.

Measurements:

Version	Compile time (full build with -j 2)	Resulting total object file size	Replay time (32M blocks)
6a57bd9 (develop)	4905.86user 142.54system 45:36.04elapsed 184%CPU (0avgtext+0avgdata 5910336maxresident)k 5883632inputs+36297912outputs (621major+79699588minor)pagefaults	1930514440	4494s
275e5bf (this branch)	2995.77user 109.49system 27:34.96elapsed 187%CPU (0avgtext+0avgdata 3329756maxresident)k 400912inputs+30901272outputs (323major+60177298minor)pagefaults	1129394680	4399s

Note: Requires changes in fc as well - bitshares/bitshares-fc#133

[oxarbitrage]

nice! is the 40% build time reduction only in windows or all ?

[pmconrad]

Measured on my linux desktop. Don't have a windows machine to test with.

[abitmore]

@cwyyprog try this?

[pmconrad]

The fc bump includes the fix for #1688

[oxarbitrage]

I made a test and i was not able to get a 40% faster build in Ubuntu 18.04 but just a 15% .

develop branch:

real	77m46,590s
user	74m55,983s
sys	2m37,780s

pull request:

real	66m3,149s
user	63m3,007s
sys	2m32,247s

Also, did you made snapshots of the 2 at block 32M. I think it might worth it.

[pmconrad]

Snapshot comparison at 37.9M blocks produced empty diff.