ActBook: Hevm section seems outdated

I tried the example in [Hevm section of ActBook](https://ethereum.github.io/act/hevm.html).

The command in the book
```
act hevm --spec src/simple.act --soljson out/dapp.sol.json
```
did not work because --soljson option seems outdated and also it should have --contract option.
Then I tried
```
act hevm --spec xxx.act --sol xxx.sol --contract Simple
```
but I got the following:
```
Checking if constructor results are equivalent.
Found 1 total pairs of endstates
Asking the SMT solver for 1 pairs
Reuse of previous queries was Useful in 0 cases
Not equivalent.

-----

The following input results in different behaviours
Calldata:
Any

Transaction Context:
CallValue: 0x0
```
I thought this was because the second line of EVM should have been `uint val = 0;`, so I replaced it, but then I got
```
Checking if constructor results are equivalent.
Found 1 total pairs of endstates
Asking the SMT solver for 0 pairs
Reuse of previous queries was Useful in 0 cases
No discrepancies found
Checking if constructor input spaces are the same.
Not equivalent.

-----

The following inputs are accepted by Act but not EVM
Calldata:
Any

Transaction Context:
CallValue: 0x2
```
Now I have no idea why this is happening.

Start with the Hevm section of ActBook at ethereum.github.io/act/hevm.html and reproduce the documented and replacement act hevm commands against the current CLI. Check the current option names and the example's Solidity input, then update the section so its command and explanation match current behavior and the example completes without unexplained discrepancies.

Written by the indexing model from the issue text.