Read log file after given line

### Expected Behaviour
It would be nice to have some mechanism to say that we want to parse logs after some line inside our file

### Actual Behaviour
Right now log-parser does not have this mechanism

No file, test, or entry point is named. Start by locating the log-reading and parsing APIs, then clarify how a line is identified and where the starting point is supplied; done means logs can be parsed beginning after the requested line and the behavior is covered by tests.

Written by the indexing model from the issue text.