feature: improve context err

[ChrisCho-H]

919bc4b

• use ImpossibleSatisfaction when op_count is None instead of MaxOpCountExceeded.

51a50ae

• unify error message for satisfaction-kind error and scriptPubKey-kind error so that these error can contain max(limit) with what it got(actual).

[apoelstra]

In c197c0b:

Can you change "{} items more than limit {}" to "{} items (limit: {})` or something? As written it sounds like we're exceeding the limit by the given amount, rather than exceeding the limit with the given amount.

Otherwise this looks great. Thanks for cleaning these up!

[ChrisCho-H]

faf16fd

• changed the err message which might be misleading!

[apoelstra]

ACK faf16fd; successfully ran local tests