Simple and secure line iterators

Simple line iterator which prevents OutOfMemory if an attacker inputs very long sequences without a delimiter by applying a max_capacity. The implementation reuses the last Rc on calling next() if it isnt used anymore.

It currently uses the linebuffer library under the hood but provides a much simpler interface with fewer pitfalls: - Incomplete lines result in Err(Incomplete>) to force users to think about this scenario - Ok variant should be compatible with std::io::BufReader beside wrapping in Rc - Invalid UTF8 results in Err(Encoding)

cargo bench (version 0.0.1)

Tests performed using 'DickensCharlesPickwick_Papers.xml', which is 34.4 MB big and 845k lines long.

Bacbook Pro 2019 2.6 GHz 6-Core Intel Core i7

``` simplelines::LineIterable::linesrc() time: [48.811 ms 49.312 ms 49.827 ms change: [+0.2107% +1.4272% +2.6542%] (p = 0.02 < 0.05) Change within noise threshold. Found 1 outliers among 100 measurements (1.00%) 1 (1.00%) high mild

Benchmarking std::BufReader::lines(): Warming up for 3.0000 s std::BufReader::lines() time: [125.78 ms 127.73 ms 129.82 ms]
change: [-3.1501% -1.3464% +0.6779%] (p = 0.17 > 0.05) No change in performance detected. Found 16 outliers among 100 measurements (16.00%) 4 (4.00%) high mild 12 (12.00%) high severe

linereader::LineReader().next_line() time: [43.261 ms 43.480 ms 43.714 ms] change: [+4.2718% +5.0450% +5.8169%] (p = 0.00 < 0.05) Performance has regressed. Found 4 outliers among 100 measurements (4.00%) 2 (2.00%) high mild 2 (2.00%) high severe ```