FarNet "script assembly" support

[nightroman]

FarNet 6.0.18 in addition to FarNet modules supports FarNet scripts. In spite
of the name, scripts are usual assemblies with methods called by the command
fn:.

It's the first step. FarNet will provide tools for building from sources on the
fly. Then FarNet scripts will be closer to what "scripts" usually mean.

See README for details.

Sample scripts:

• C# sample, more details
• F# sample, very basic

Scripts vs. modules

Pros:

• Script commands are simpler to create, especially with parameters.
• Scripts may be unloaded, changed, invoked without restarting.
• Scripts do not add any overhead to FarNet when not used.

Cons:

• Scripts may only have commands invoked by the common prefix fn:.
• fn: syntax is somewhat verbose for manual typing.
• Missing FarNet support for language files.
• Limited FarNet support for help files.

Scripts vs. alternatives

The known and considered alternatives are:

• Roslyn
• CS-Script

Roslyn would be suitable for simple REPL scenarios but not so good for complex.
But for REPL, FarNet.PowerShellFar is arguably easier to use and more powerful.

CS-Script is more suitable for complex scripts but still has various limitations.
Multiple sources may have conflicting using statements, NuGet support is limited.

Roslyn and CS-Script do not have natural or straightforward debugging support.
Moving or sharing source files between modules and scripts is more difficult.

In contrast, FarNet scripts are technically not scripts. They have no limitations.
They may be complex, with dependencies (NuGet, projects) and usual debugging.
The price for that is script building, manual now but somehow automated eventually.
On the other hand, compiled scripts are better for performance in the long term.

[nightroman]

FarNet 6.0.20 - modules may have fn-methods as well. They are called using the similar syntax:

fn: module=<name>; method=<name> ...