Added StructuredModel::structured_labels_factory() to create the right SO labels class.
Prepared StructuredLabels' methods for overloading.
Overloading add_label, set_label, get_label, get_num_elements in MulticlassSOLabels.
Added own storage object for real labels.
Temporarily disabled ensure_valid calls.
Fixed memory leak (forgot freeing of new CRealNumber labels).
Fix wrong indentation in LabelsFactory::get_name
Merge pull request #1775 from iglesias/develop

Fix wrong indentation in LabelsFactory::get_name
when mldata.org cannot be accessed w/o error - don't let the example fail
Minor style and doc fixes in StringFeatures
Merge pull request #1776 from iglesias/develop

Minor style and doc fixes in StringFeatures
Update Java requirements
Merge pull request #1778 from iglesias/develop

Update Java requirements
Change directory contents to contents in README to fix section link
Merge pull request #1780 from iglesias/develop

Change directory contents to contents in README to fix section link
Add Dockerfile for trusted builds on index.docker.io
Merge pull request #1774 from tklein23/solabels_factory_in_somodel

Structured model refactoring: Added factory for specific labels
Fix assertion - open() can return "0", which is a valid file descriptor.
Merge pull request #1782 from tklein23/develop

Fix assertion - open() can return "0", which is a valid file descriptor.
svm/OnlineLibLinear: Added learning of StreamingSparseFeatures:
* Added method "train_one" for sparse vectors (a lot code duplication!  sorry!)
* "train_example" now consumes CStreamingDenseFeatures and CStreamingSparseFeatures
* Added bounds checking in CStreamingSparseFeatures<T>::dense_dot
  (allowing sparse dot-product with shorter weight vector)

Refactoring in StreamingSparseFeatures
* removed duplicate "expand_if_required" - already implemented in features
* avoided manual resizing of vectors using low-level stuff like realloc/memset/etc.
Move all md files but README to doc/md
Merge pull request #1786 from iglesias/markdown

Move all md files but README to doc/md