Only add executables from itch (#48)

The Itch db can refer to multiple files,
before the first one added was selected,
now the first one that is  executable is selected.

Cargo.lock

@@ -95,6 +95,7 @@ dependencies = [
  "fltk",
  "fltk-theme",
  "futures",
+ "is_executable",
  "nom 7.0.0",
  "nom_locate",
  "reqwest",
@@ -599,6 +600,15 @@ version = "2.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "68f2d64f2edebec4ce84ad108148e67e1064789bee435edc5b60ad398714a3a9"
 
+[[package]]
+name = "is_executable"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa9acdc6d67b75e626ad644734e8bc6df893d9cd2a834129065d3dd6158ea9c8"
+dependencies = [
+ "winapi",
+]
+
 [[package]]
 name = "itoa"
 version = "0.4.8"