Add basic serialize/deserialize benchmarks

[Turnerj]

As I mentioned in #100 , it would be a good idea to add some benchmarks to Schema.NET, specifically around the serialization/deserialization process.

While the core serialization processing might be in a third-party library (either Newtonsoft.Json or eventually System.Text.Json), there are multiple custom converters used in the library which may have their own performance bottlenecks.

The benchmarks, however, are also useful for gauging the performance improvement when going to System.Text.Json too.

I've specifically included 2 benchmarks, one testing WebSite with a fairly basic model (taken from the WebSiteTest) and one for Book (taken from BookTest). While there isn't anything to really base these numbers on at the moment, it can help for relative improvements.

I may add more specialised benchmarks, specifically targeting the ValuesJsonConverter in the future as that is where I believe the biggest gains are in the library.

BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
Intel Core i7-6700HQ CPU 2.60GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
.NET Core SDK=5.0.100-alpha1-015710
  [Host]     : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), X64 RyuJIT
  Job-MDWQYW : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), X64 RyuJIT

Runtime=.NET Core 3.0

Book Benchmark

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Serialize	175.9 us	1.05 us	0.88 us	15.3809	-	-	47.27 KB
Deserialize	445.8 us	3.48 us	3.26 us	39.0625	-	-	120.96 KB

WebSite Benchmark

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
Serialize	26.90 us	0.252 us	0.236 us	2.9297	-	-	9.16 KB
Deserialize	47.89 us	0.300 us	0.280 us	4.9438	-	-	15.17 KB

[RehanSaeed]

There are a few more useful atrributes that could be added here to generate some graphs and more stats. See https://github.com/Dotnet-Boxed/Framework/blob/master/Benchmarks/Boxed.Mapping.Benchmark/MapListBenchmark.cs

[Turnerj]

Yep, happy to add those. Do you think it is worth benchmarking multiple versions of .NET like your linked example or just leave it still as .NET Core 3?

[RehanSaeed]

.NET Framework is still used a fair bit, so I added it. The results can be very different.

[RehanSaeed]

Only one comment. Looks good apart from that.

[Turnerj]

I've added the additional benchmark settings that you've linked to. Yeah, there is a bit of a difference between .NET 4.7.2 and .NET Core 3:

BenchmarkDotNet=v0.12.0, OS=Windows 10.0.18362
Intel Core i7-6700HQ CPU 2.60GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
  [Host]     : .NET Framework 4.8 (4.8.4075.0), X64 RyuJIT
  Job-VTGAFA : .NET Framework 4.8 (4.8.4075.0), X64 RyuJIT
  Job-ZVNHQX : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), X64 RyuJIT

Method	Runtime	Mean	Error	StdDev	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
Serialize	.NET 4.7.2	160.3 us	3.04 us	2.84 us	157.4 us	165.6 us	15.3809	-	-	47.52 KB
Deserialize	.NET 4.7.2	439.2 us	3.93 us	3.49 us	434.2 us	447.0 us	38.0859	-	-	119.51 KB
Serialize	.NET Core 3.0	152.5 us	2.35 us	1.96 us	147.1 us	155.8 us	15.3809	-	-	47.27 KB
Deserialize	.NET Core 3.0	376.8 us	5.63 us	4.99 us	368.5 us	384.9 us	37.5977	-	-	116.11 KB

[RehanSaeed]

Thanks!