Detect BMP and TIFF image size

[kikihakiem]

This change is 

[kikihakiem]

It's weird it fails with go1.4 in travis. When I run test with go1.4 in my local, all tests passed

$ docker run --rm -v "$PWD":/go/src/github.com/rubenfonseca/fastimage -w /go/src/github.com/rubenfonseca/fastimage golang:1.4-alpine go version && go test ./...
go version go1.4.3 linux/amd64
ok      github.com/rubenfonseca/fastimage       2.143s

Edit: the issue was because cached response, so whichever test come later, it will use cached response from earlier test, resulting no timeout. That also explains why there's only 1 passed test matrix.