Environment is now a struct (not an interface). This
reduces a lot of tech-debt throughout the codebase where a virtual
machine environment had to be implemented in order to test or run it.
The new environment is suitable to be used en the json tests, core
consensus and light client.
that specifies the maximum number of elements in the `structLogs`
output. This option is useful for debugging a transaction that
involves a large number of repetition.
For example,
```
debug.traceTransaction(tx, {disableStorage: true, limit: 2})
```
shows at most the first two steps in the `structLogs`.
Jeffrey Wilcke
Kenji Siu
Yoichi Hirai
Nick Johnson