Update startercode branch to v2.0.0

[danforbes]

Bump #79 to v2.0.0

[zbraniecki]

I'm seeing the following error on the current nightly:

error[E0282]: type annotations needed
    --> /home/zbraniecki/.cargo/registry/src/github.com-1ecc6299db9ec823/sp-arithmetic-2.0.0/src/fixed_point.rs:541:9
     |
541  |                   let accuracy = P::ACCURACY.saturated_into();
     |                       ^^^^^^^^ consider giving `accuracy` a type
...
1595 | / implement_fixed!(
1596 | |     FixedI64,
1597 | |     test_fixed_i64,
1598 | |     i64,
...    |
1601 | |     "_Fixed Point 64 bits signed, range = [-9223372036.854775808, 9223372036.854775807]_",
1602 | | );
     | |__- in this macro invocation
     |
     = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

[jimmychu0807]

I am merging this for now, because it is better than the previous version.

But @zbraniecki, I think another upgrade to v2.0.1 will fix the issue you have.