Added EvalSession way of controlling all coroutines started from a script

docs/lyng.io.fs.md

@@ -39,23 +39,27 @@ This brings in:
 
 ---
 
-#### Install the module into a Lyng Scope
+#### Install the module into a Lyng session
 
-The filesystem module is not installed automatically. You must explicitly register it in the scope’s `ImportManager` using the installer. You can customize access control via `FsAccessPolicy`.
+The filesystem module is not installed automatically. The preferred host runtime is `EvalSession`: create the session, get its underlying scope, install the module there, and execute scripts through the session. You can customize access control via `FsAccessPolicy`.
 
 Kotlin (host) bootstrap example:
 
 ```kotlin
+import net.sergeych.lyng.EvalSession
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.io.fs.createFs
 import net.sergeych.lyngio.fs.security.PermitAllAccessPolicy
 
-val scope: Scope = Scope.new()
-val installed: Boolean = createFs(PermitAllAccessPolicy, scope)
-// installed == true on first registration in this ImportManager, false on repeats
+suspend fun bootstrapFs() {
+    val session = EvalSession()
+    val scope: Scope = session.getScope()
+    val installed: Boolean = createFs(PermitAllAccessPolicy, scope)
+    // installed == true on first registration in this ImportManager, false on repeats
 
-// In scripts (or via scope.eval), import the module to use its symbols:
-scope.eval("import lyng.io.fs")
+    // In scripts (or via session.eval), import the module to use its symbols:
+    session.eval("import lyng.io.fs")
+}
 ```
 
 You can install with a custom policy too (see Access policy below).
@@ -185,7 +189,7 @@ val denyWrites = object : FsAccessPolicy {
 }
 
 createFs(denyWrites, scope)
-scope.eval("import lyng.io.fs")
+session.eval("import lyng.io.fs")
 ```
 
 Composite operations like `copy` and `move` are checked as a set of primitives (e.g., `OpenRead(src)` + `Delete(dst)` if overwriting + `CreateFile(dst)` + `OpenWrite(dst)`).