Ignore_errors flag to work in a relaxed mode

[kavitharaju]

In v2.x we had relaxed mode where users were allowed to work with "not-perfect" usfm files and still manage to get maximum content out of it.

To bring in that kind of a feature in V3.x, use a flag to ignore errors in conversion APIs.
Even when there are errors after parsing, the conversion APIs like to_dict(), to_usx(), to_list() etc should work and provide output from all portions where it parsed successfully, when used with this flag. Otherwise it should indicate there are errors.

This feature should behave alike on CLI and in code.