Testing with Docker

[WolfgangFahl]

I'd love to try out pull request and other changes in a virtual environment before working on the main repository.
see #434 for a start and
https://stackoverflow.com/questions/27567846/how-can-i-check-out-a-github-pull-request-with-git for getting pull request

[WolfgangFahl]

scripts/rundocker dev
root@58b9cbc590b4:/usr/src/justpy# scripts/pull 401
assuming this is in docker 58b9cbc590b4
setting git config user.email to allow pull
remote: Enumerating objects: 8, done.
remote: Counting objects: 100% (8/8), done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 8 (delta 6), reused 8 (delta 6), pack-reused 0
Unpacking objects: 100% (8/8), 1.11 KiB | 284.00 KiB/s, done.
From https://github.com/elimintz/justpy
 * branch            refs/pull/401/head -> FETCH_HEAD
Merge made by the 'recursive' strategy.
 examples/multiuploads.py              | 15 +++++++++++++++
 justpy/templates/js/html_component.js | 40 ++++++++++++++++++++--------------------
 2 files changed, 35 insertions(+), 20 deletions(-)
 create mode 100644 examples/multiuploads.py
diff --git a/examples/multiuploads.py b/examples/multiuploads.py
new file mode 100644
index 0000000..724da53
--- /dev/null
+++ b/examples/multiuploads.py
@@ -0,0 +1,15 @@
+from justpy import *
+
+def on_submit(c, msg):
+    print(len(msg.form_data[0]["files"][0]["file_content"]))
+    print(len(msg.form_data[1]["files"][0]["file_content"]))
+
+def multi_uploads():
+    wp=WebPage()
+    form=Form(a=wp, submit=on_submit)
+    Input(type="file", name="f1", a=form)
+    Input(type="file", name="f2", a=form)
+    Input(type="submit", value="OK", a=form)
+    return wp
+
+justpy(multi_uploads)
\ No newline at end of file
diff --git a/justpy/templates/js/html_component.js b/justpy/templates/js/html_component.js
index 64bea2a..6ba33ab 100644
--- a/justpy/templates/js/html_component.js
+++ b/justpy/templates/js/html_component.js
@@ -81,11 +81,7 @@ Vue.component('html_component', {
                 event.stopPropagation();
                 var form_elements_list = [];
                 var form_elements = form_reference.elements;