fix: Ease clap2->clap3 migration with deprecations

Fixes clap-rs#2617

src/build/arg/mod.rs

@@ -311,6 +311,12 @@ impl<'help> Arg<'help> {
         }
     }
 
+    /// Deprecated, see [`Arg::new`]
+    #[deprecated(since = "3.0.0", note = "Replaced with `Arg::new`")]
+    pub fn with_name<S: Into<&'help str>>(n: S) -> Self {
+        Self::new(n)
+    }
+
     pub(crate) fn generated(mut self) -> Self {
         self.provider = ArgProvider::Generated;
         self
@@ -666,6 +672,12 @@ impl<'help> Arg<'help> {
         self
     }
 
+    /// Deprecated, see [`Arg::about`]
+    #[deprecated(since = "3.0.0", note = "Replaced with `Arg::about`")]
+    pub fn help(self, h: &'help str) -> Self {
+        self.about(h)
+    }
+
     /// Sets the long help text of the argument that will be displayed to the user when they print
     /// the help information with `--help`. Typically this a more detailed (multi-line) message
     /// that describes the arg.
@@ -738,6 +750,12 @@ impl<'help> Arg<'help> {
         self
     }
 
+    /// Deprecated, see [`Arg::long_about`]
+    #[deprecated(since = "3.0.0", note = "Replaced with `Arg::long_about`")]
+    pub fn long_help(self, h: &'help str) -> Self {
+        self.long_about(h)
+    }
+
     /// Set this arg as [required] as long as the specified argument is not present at runtime.
     ///
     /// **Pro Tip:** Using `Arg::required_unless_present` implies [`Arg::required`] and is therefore not
@@ -4392,6 +4410,15 @@ impl<'help> Arg<'help> {
         }
     }
 
+    /// Deprecated, see [`Arg::multiple_occurrences`] and [`Arg::multiple_values`]
+    #[deprecated(
+        since = "3.0.0",
+        note = "Broken out into `Arg::multiple_occurrences` and `Arg::multiple_values`"
+    )]
+    pub fn multiple(self, multi: bool) -> Self {
+        self.multiple_occurrences(multi).multiple_values(multi)
+    }
+
     /// Indicates that all parameters passed after this should not be parsed
     /// individually, but rather passed in their entirety. It is worth noting
     /// that setting this requires all values to come after a `--` to indicate they