Allow multiple level sets, pull out default order into "sequence" file

levels/bottom-up/blob-create/congrats

@@ -0,0 +1,5 @@
+Tip: You can also use a command like this to create a blob in a single line:
+
+    echo "awesome content" | git hash-object -w --stdin
+
+Did you already notice that you can drag and drop all objects? :)

levels/bottom-up/blob-create/description

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+At its core, Git is very simple. It stores "objects", which are basically files identified by an "identifier" (short: ID).
+
+There are four types of objects: blobs, trees, commits, and tags. The simplest type is a "blob", which is just a piece of text.
+
+Let's create some blobs! To do that, create a file with the desired content, and then use
+
+    git hash-object -w <file>
+
+The flag -w means "write", and tells Git to actually write the new blob to the disk.
+
+Create three new blobs!

levels/bottom-up/blob-create/goal

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+echo "Hi" > file1
+echo "Ho" > file2
+echo "Hu" > file3
+git hash-object -w file1
+git hash-object -w file2
+git hash-object -w file3

levels/bottom-up/blob-create/win

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+BLOB_COUNT=$(git cat-file --batch-check='%(objectname) %(objecttype)' --batch-all-objects | grep blob | wc -l)
+
+test "$BLOB_COUNT" -gt 2