smartly detect what case style should be used in `duplicate line and insert content`

[MohammadMD1383]

this can be done by:

• checking file type
• context where replacement happens

[MohammadMD1383]

what's your idea about it? @JasonGmitter

[j-a-s-o-n-g]

Sure, this could be enabled/disabled by the global "Preserve case" option that effects all of the other commands.