[Feature Request] Default to file when using './' or '/'

[jdorel]

To read from a file, currently we need to specify -i.

Could we detect that the first characters are either / or ./ to read from a file ? So that we could use trans ./file or trans /home/user/file.

[soimort]

Alternatively one can use the file:// scheme for specifying a file.

Currently the use of prefix / conflicts with the syntax of engine selecting (see #103). This default behavior may not be changed any time soon.