feat(single-instance): Add semver compatibility check for Windows and Linux (#502)

* added semver compatibility check for Windows and Linux

* fixed formatting

* put semver feature behind a feature flag

* remove semver from root manifest

* linux compile error

* docs: Add mention for semver feature in readme

---------

Co-authored-by: FabianLars <fabianlars@fabianlars.de>

plugins/single-instance/src/semver_compat.rs

@@ -0,0 +1,17 @@
+#![cfg(feature = "semver")]
+
+/// Takes a version and spits out a String with trailing _x, thus only considering the digits
+/// relevant regarding semver compatibility
+pub fn semver_compat_string(version: semver::Version) -> String {
+    // for pre-release always treat each version separately
+    if !version.pre.is_empty() {
+        return version.to_string().replace(['.', '-'], "_");
+    }
+    match version.major {
+        0 => match version.minor {
+            0 => format!("0_0_{}", version.patch),
+            _ => format!("0_{}_x", version.minor),
+        },
+        _ => format!("{}_x_x", version.major),
+    }
+}