Implement async download based on chronos

- implementation of async download based on chronos asyncproc
- the PR is based on nim-lang#938

Author: bobeff

.gitignore

@@ -62,3 +62,6 @@ src/nimblepkg/version
 # Test procedure artifacts
 *.nims
 /buildTests
+/nimble.develop
+nimble.paths
+*.paths

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "nim-bearssl"]
+	path = nim-bearssl
+	url = ./nim-bearssl
+[submodule "nim-chronos"]
+	path = nim-chronos
+	url = ./nim-chronos
+[submodule "nim-stew"]
+	path = nim-stew
+	url = ./nim-stew

changelog.markdown

@@ -12,6 +12,7 @@ This is a major release containing four new features:
 - Download tarballs when downloading packages from GitHub.
 - A setup command.
 - Added a `--package, -p` command line option.
+- Parallel downloads of the locked dependencies.
 
 ## 0.13.0
 

nim-bearssl

@@ -11,7 +11,8 @@ installExt = @["nim"]
 
 # Dependencies
 
-requires "nim >= 0.13.0"
+requires "nim >= 0.13.0", "chronos", "bearssl", "stew"
+
 
 when defined(nimdistros):
   import distros