v0.7.0

Changes

• get_grades() returns the current term's Grades: grades newest first (mark, weight, category, topic, teacher, entered date, subject and code) and subjects with teacher and attendance. Grades.average(course_id) weights each grade by its weight; marks other than 1–5 are kept as text and left out. Grade.short / Subject.short give the subject abbreviation ("Aj").
• The current term is chosen by its heading ("2. pololetí" over "1. pololetí"). A grades page whose rows can't be read raises ParseError instead of returning no grades.
• CAPTURE_PAGES gains evaluation_overall, to catch the term report's markup once it is published.
• scripts/capture_fixtures.py --evaluation saves the grades pages for building parsers.