Flexible length for the chunk "sub identifier"

[oliverpool]

Hi,

Thank you for this great tool!

I prefer to re-assemble the file using system tools (like cat chunk_* > complete_file), but the ordering is wrong because chunk_10 is sorted before chunk_2. I would like the "sub-identifier" to be padded : chunk_02.

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This PR proposes a new parameter: $pad_length.

Using this parameter, one can choose a minimum length of the "sub-identifier". I also added an optional parameter to getChunkPath, because I intend to call getChunkPath('*', 0) to get the file pattern for my cat command.

I need your help to determine the best way to set the "global" $pad_length: should I use the ConfigInterface and add a parameter there ?

[coveralls]

Coverage decreased (-1.4%) to 98.63% when pulling c04a639 on oliverpool:sub-identifier-padding into b9da114 on flowjs:master.

[AidasK]

It should be added to the Config class. Make sure you don't break other implementations. I think this should be released as a major version, because it can break code for others. Don't forget the tests, code coverage should be 100%

[oliverpool]

It should be added to the Config class

Ok, I'll work on it.

I think this should be released as a major version, because it can break code for others.

If we set the default pad_length to 0, it shouldn't break anything.

Don't forget the tests

Sure, I'll look at it.

[AidasK]

Adding a new method to a config interface is a BC. Because users might have used it in their own classes.