Automate cancer-data download from figshare (cognoma#42)

`1.download.ipynb` queries the figshare API to find the latest versions of the
files and downloads them.

Changes directory for storing downloaded data from `data` to `download`,
following the convention of cognoma/cancer-data.

Add `requests` library to environment.

Add an execute script that executes notebooks in the root directory in order
and exports them to scripts.

In `algorithms`, notebooks were not updated besides `SGDClassifier-master.ipynb`
which is the example notebook and template for new implementations.

.gitignore

@@ -2,5 +2,4 @@
 .ipynb_checkpoints
 
 # Large downloaded data files
-data/expression.tsv.bz2
-data/mutation-matrix.tsv.bz2
+download/