Allow formatting from stdin

[silversquirl]

Most other code formatters support reading code from stdin and outputting formatted code to stdout. This is a very useful standard interface for code formatters, and allows very easy integration with editors, such as through Kakoune's formatcmd option.

Since Rome can format multiple types of files, it needs to detect the filetype somehow; currently it uses the file extension for this, which would be incompatible with formatting from stdin. Options for handling this include a flag to specify the filetype from the command line (eg. rome format --stdin --filetype js), which would allow rome to benefit from the editor's detection; or copy what Prettier does and use a flag to specify the filename of the data provided on stdin (eg. rome format --stdin --stdin-filename hello.js).

[ematipico]

Great suggestion! Yes, I suppose it makes sense to have some argument like this!