Merge pull request #577 from FerhatMihoubi/master

2 additional commits
Release notes for 4.4.1
Fix octave versions.
Fixed bug (a string passed to a dseries object can be a date).
Fixed bug. Allow selection of an observation with a date defined in a formatted string.
Implement broadcasting for operations (+,-,* and /) between dseries and scalar or vectors. Efficiency and cosmetic changes.
Allow assignation of variables in an empty dseries object.
Fixed typo in manual.
Update manual according to commit 117f338effd2dd64021666a3f1bc610058c0b7e8.
Finalize release notes for 4.4.1.
Fixed example ep/rbcii.mod (RBC model with endogenous labour supply and irreversible investment).

The leaded lagrange multiplier (associated with the positivity constraint on investment) was missing in the Euler equation.
Minor fix to release announcement.
doc fix typo
dseries: allow assign to select by date string as opposed to dates
remove unused variable
Adds setdiff method to dates
Corrects a typo, checks that the number of dates and the number of values are equal, Warns instead of reporting an error if the basic_plan is applied on a shock that is used in a flip_plan (flip_plan has the higher priority)