Try to make v4l optional when compiling lib only

Cargo.toml

@@ -4,11 +4,14 @@ version = "0.1.0"
 authors = ["Ruben van de Ven <git@rubenvandeven.com>"]
 edition = "2018"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[features]
+build-binary = ["v4l"] 
 
 [[bin]]
 name = "visual_haarcascades"
 path = "src/main.rs"
+required-features = ["build-binary"]     # https://stackoverflow.com/a/46017284
 
 [[bin]]
 name = "visual_haarcascades_test"
@@ -22,7 +25,7 @@ crate-type = ["dylib"]
 [dependencies]
 nannou = "0.14"
 # clang-sys = "0.29.3"
-v4l = {version = "0.5.1", features = ["libv4l"]}
+v4l = {version = "0.5.1", features = ["libv4l"],  optional = true}
 image = "0.23"
 log = "0.4"
 xml-rs = "0.8.3"

src/test.rs

@@ -5,7 +5,6 @@ extern crate stopwatch;
 use stopwatch::{Stopwatch};
 
 use simplelog::*;
-use v4l::{Buffer, CaptureDevice, MappedBufferStream};
 use image;
 
 mod visualhaar;
@@ -13,8 +12,6 @@ mod heatmap;
 
 // use std::fs::File;
 
-static mut CAMERA: Option<CaptureDevice> = None;
-
 fn main() {
     CombinedLogger::init(
         vec![