workspace::get should not iterate all workspaces

[matthias-t]

My fault, sorry.

workspace/src/workspace.rs

Lines 60 to 73 in 3c6848c

	pub fn get(name: &str) -> Option<Workspace> {
	paths()
	.into_iter()
	.filter(|path| {
	let file_stem = path.file_stem();
	if file_stem.is_none() {
	return false;
	}
	file_stem.unwrap().to_string_lossy() == name
	})
	.map(read)
	.map(parse)
	.nth(0)
	}

Instead it should only try to read from ~/workspace/NAME.toml. That implies moving workspace::Workspace::data_path(&self) to something like workspace::file_path(name: &str).