add exa package (#3374)

* add exa package

adds exa (ls replacement) v0.9.0 package file

* fix exa package module depends

removes cmake as already a core dependency and sets
rust as only a build dependency

packages/exa.rb

+require 'package'
+
+class Exa < Package
+  description 'Modern replacement for \'ls\''
+  homepage 'https://the.exa.website'
+  version '0.9.0'
+  source_url 'https://github.com/ogham/exa/archive/v0.9.0.tar.gz'
+  source_sha256 '96e743ffac0512a278de9ca3277183536ee8b691a46ff200ec27e28108fef783'
+
+  depends_on 'rust' => :build
+  depends_on 'libgit2'
+
+  def self.build
+    case ARCH
+    when 'aarch64'
+      system 'rustup toolchain install 1.25.0-aarch64-unknown-linux-gnu'
+      system 'rustup default 1.25.0-aarch64-unknown-linux-gnu'
+    when 'armv7l'
+      system 'rustup toolchain install 1.25.0-armv7-unknown-linux-gnueabihf'
+      system 'rustup default 1.25.0-armv7-unknown-linux-gnueabihf'
+    else
+      system 'rustup toolchain install stable'
+      system 'rustup default stable'
+    end
+    system 'cargo build --release'
+  end
+
+  def self.check
+    system 'cargo test --all'
+  end
+
+  def self.install
+    system "install -Dm755 target/release/exa #{CREW_DEST_PREFIX}/bin/exa"
+  end
+end