Serilog Sinks Rollingfile Versions Save

• #37 - Multiprocess shared files on .NET Core

• #29 - {Hour} and {HalfHour} specifiers
• #32 - Don't try checking exception HRESULTs on .NET Core

• serilog/serilog-sinks-file#18 - periodic flush to disk option

• #24

• #15 - multi-process shared files

#11 - Default encoding without BOM

Adds overload to specify formatter.

Initial version moved from the Serilog package. Targets .NET 4.5+ and .NET Core 1.0.