Add Neural Network Example (#312)

* Add Neural Network Example

* reduce the number of samples. this is just an example

* correctly output the error

* fix warnings

Co-authored-by: Michael McCulloch <michael.james.mcculloch@fastmail.com>

Author: MichaelMcCulloch

Cargo.toml

@@ -53,6 +53,7 @@ libc = "0.2"
 num  = "0.4.0"
 lazy_static = "1.0"
 half = "1.5.0"
+mnist = {version="0.5.0", features = ["download"]}
 serde = { version = "1.0", features = ["derive"], optional = true }
 
 [dev-dependencies]
@@ -101,3 +102,8 @@ path = "examples/fft.rs"
 [[example]]
 name = "using_half"
 path = "examples/using_half.rs"
+
+[[example]]
+name = "neural_network"
+path = "examples/neural_network.rs"
+