fn_trait library

This trait provide helper function and macro called chain to ease chaining of function where output of first function piped directly as input to another function and so forth.

Use case 1 - Macro chain

```rust use fn_chain::chain;

fn simple_add(a : i32, b : i32, c : i32) -> i32 { a + b + c }

fn pass_through(v : f64) -> f64 { v }

asserteq!( 6f64, chain!( simpleadd(1, 2, 3), |result: i32| {(result as f64).powi(2)}, |sqr: f64| {sqr.powf(0.5)}, passthrough, passthrough ) ); ```

Use case 2 - function chain

```rust use fn_chain::chain;

fn simple_add(a : i32, b : i32, c : i32) -> i32 { a + b + c }

fn pass_through(v : f64) -> f64 { v }

asserteq!(6f64, *chain(simpleadd(1, 2, 3)) .chain(|result| {(result as f64).powi(2)}) .chain(|sqr| sqr.powf(0.5)) .chain(passthrough) .chain(passthrough)); ```