Replace bools in public API with enums

[jariq]

Since we are already breaking assembly reference compatibility in #52 I am also going to explore the possibility of making API more user friendly.

This PR replaces several most annoying occurrences of bool type in public APIs with enum types. I believe that code with enums is not only easier to write but most importantly it is much easier to read.

Five new enums have been introduced:

1 - Net.Pkcs11Interop.Common.AppType

Previous code that initializes unmanaged PKCS#11 library in multi-threaded applications:

Pkcs11 pkcs11 = new Pkcs11("pkcs11-mock-x64.dll", true);

Current code that initializes unmanaged PKCS#11 library in multi-threaded applications:

Pkcs11 pkcs11 = new Pkcs11("pkcs11-mock-x64.dll", AppType.MultiThreaded);

2 - Net.Pkcs11Interop.Common.InitType

Previous code that initializes unmanaged PKCS#11 library with function pointers acquired with a single call of C_GetFunctionList function:

Pkcs11 pkcs11 = new Pkcs11("pkcs11-mock-x64.dll", true, true);

Current code that initializes unmanaged PKCS#11 library with function pointers acquired with a single call of C_GetFunctionList function:

Pkcs11 pkcs11 = new Pkcs11("pkcs11-mock-x64.dll", AppType.MultiThreaded, InitType.WithFunctionList);

3 - Net.Pkcs11Interop.Common.SlotsType

Previous code that obtains list of slots with token present:

List<Slot> slots = pkcs11.GetSlotList(true);

Current code that obtains list of slots with token present:

List<Slot> slots = pkcs11.GetSlotList(SlotsType.WithTokenPresent);

4 - Net.Pkcs11Interop.Common.WaitType

Previous code that analyzes slot events in non-blocking mode:

pkcs11.WaitForSlotEvent(true, out bool eventOccured, out ulong slotId);

Current code that analyzes slot events in non-blocking mode:

pkcs11.WaitForSlotEvent(WaitType.NonBlocking, out bool eventOccured, out ulong slotId);

5 - Net.Pkcs11Interop.Common.SessionType

Previous code that opens new read-only session:

Session session = slot.OpenSession(true);

Current code that opens new read-only session:

Session session = slot.OpenSession(SessionType.ReadOnly);