add cli interface

Implements #1

README.md

···
 ```
 
 ### As CLI tool
-
-TODO: yet to be implemented
+```bash
+gleam run -m run ./examples/helloworld.bf
+#> Hello World!
+```

gleam.toml

···
 [dependencies]
 gleam_stdlib = ">= 0.44.0 and < 2.0.0"
 splitter = ">= 1.1.0 and < 2.0.0"
+argv = ">= 1.0.2 and < 2.0.0"
+simplifile = ">= 2.3.0 and < 3.0.0"
 
 [dev-dependencies]
 gleeunit = ">= 1.0.0 and < 2.0.0"

manifest.toml

···
 # You typically do not need to edit this file
 
 packages = [
+  { name = "argv", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "argv", source = "hex", outer_checksum = "BA1FF0929525DEBA1CE67256E5ADF77A7CDDFE729E3E3F57A5BDCAA031DED09D" },
+  { name = "filepath", version = "1.1.2", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "filepath", source = "hex", outer_checksum = "B06A9AF0BF10E51401D64B98E4B627F1D2E48C154967DA7AF4D0914780A6D40A" },
   { name = "gleam_stdlib", version = "0.65.0", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "7C69C71D8C493AE11A5184828A77110EB05A7786EBF8B25B36A72F879C3EE107" },
   { name = "gleeunit", version = "1.6.1", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "FDC68A8C492B1E9B429249062CD9BAC9B5538C6FBF584817205D0998C42E1DAC" },
+  { name = "simplifile", version = "2.3.0", build_tools = ["gleam"], requirements = ["filepath", "gleam_stdlib"], otp_app = "simplifile", source = "hex", outer_checksum = "0A868DAC6063D9E983477981839810DC2E553285AB4588B87E3E9C96A7FB4CB4" },
   { name = "splitter", version = "1.1.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "splitter", source = "hex", outer_checksum = "05564A381580395DCDEFF4F88A64B021E8DAFA6540AE99B4623962F52976AA9D" },
 ]
 
 [requirements]
+argv = { version = ">= 1.0.2 and < 2.0.0" }
 gleam_stdlib = { version = ">= 0.44.0 and < 2.0.0" }
 gleeunit = { version = ">= 1.0.0 and < 2.0.0" }
+simplifile = { version = ">= 2.3.0 and < 3.0.0" }
 splitter = { version = ">= 1.1.0 and < 2.0.0" }

src/run.gleam

···
+import argv
 import gbf
 import gleam/io
+import simplifile
 
 pub fn main() -> Nil {
-  let input =
-    "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++."
+  case argv.load().arguments {
+    [filename] -> {
+      let assert Ok(source) = simplifile.read(filename)
+      let assert Ok(virtual_machine) = gbf.run(source)
 
-  let assert Ok(virtual_machine) = gbf.run(input)
-
-  virtual_machine
-  |> gbf.output
-  |> io.println
+      virtual_machine
+      |> gbf.output
+      |> io.println
+    }
+    _ -> io.println("usage: ./program filename.bf")
+  }
 }