main: add more routes for pretty pasting

cleaned up code and added a route for signifying code language
explicitly at `/p/<filename>.<ext>`
Also async-ified the server after upgrading Rocket to 0.5-rc1

Signed-off-by: Gunwant Jain <mail@wantguns.dev>

Cargo.toml

@@ -6,7 +6,11 @@ edition = "2018"
 
 [dependencies]
 rand = "0.8.0"
-rocket = "0.4.6"
-rocket_contrib = { version = "0.4.6", features = ["tera_templates"] }
+rocket = "0.5.0-rc.1"
 tree_magic = "0.2.3"
+syntect = "4.5.0"
+
+[dependencies.rocket_dyn_templates]
+version = "0.1.0-rc.1"
+features = ["tera"]