Update to Substrate v2.0.0

[LaurentTrk]

There has been some changes between the Substrate 2.0.0-rc6 and the final one, that need to be reported in this rpc client:

• Use metadata V12
• Change RefCount Account type (u32 Refcounts, plus migration paritytech/substrate#7164)

I hope I've done things right ;)

[LaurentTrk]

Need to work on travis tests...

[codecov]

Codecov Report

Merging #100 into master will increase coverage by 0.06%.
The diff coverage is 59.48%.

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
+ Coverage   57.70%   57.77%   +0.06%     
==========================================
  Files          92       93       +1     
  Lines        3114     3230     +116     
==========================================
+ Hits         1797     1866      +69     
- Misses        962      987      +25     
- Partials      355      377      +22     

Impacted Files	Coverage Δ
types/metadataV12.go	52.52% <52.52%> (ø)
types/metadata.go	71.73% <100.00%> (+3.97%)	⬆️

---

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 305d63b...0e9198a. Read the comment docs.

[mikiquantum]

@LaurentTrk LGTM! Thanks for the contribution. Only one comment about removing support for v1 in the Makefile. I will merge up after that.

[mikiquantum]

@LaurentTrk that is very interesting, I can label the PR, Do you have any more information that I can link as well to the PR && issue?

[LaurentTrk]

No more information, the label is enough. Thanks !!

Pretty sure you know about Hacktoberfest, but just in case https://hacktoberfest.digitalocean.com/