Custom .json should be supported in subdirectories

[jgouly]

Currently the .json files need to be in the same directory that 'xargo' is run in.

I want to organise the .json files to be in other directories.

[japaric]

@jgouly It seems you can use the RUST_TARGET_PATH env variable (this is a rustc specific env variable) for this. For example:

$ export RUST_TARGET_PATH=~/rust/targets/

$ ls ~/rust/targets/*.json
/home/japaric/rust/targets/cortex-m3.json

$ ls *.json
zsh: no matches found: *.json

$ rm -rf ~/.xargo
$ xargo clean
$ xargo build --target cortex-m3 --verbose && echo OK
(..)
OK

EDIT: This was tested with Xargo 0.1.8.