Allow the cdxj used for replay to be modified at runtime

[machawk1]

See #117

[ibnesayeed]

Usually system signals are being used to reload configurations. However, if the index data is not in memory, instead it is read from the file each time then updating the same file should just work (as long as the inode does not change).

[machawk1]

@ibnesayeed There exists the scenario where the cdxj may never be in a file (i.e., if piped). The ticket for this task is not difficult to accomplished and the same functions can be used, I just have yet to tie it all together for this TODO.