Removing support to Python 2 (for Lea 4)

[Pierre Denis]

The Lea project, started more than 10 years ago, supports Python versions 2.6, 2.7 and 3.x. The support of Python 2 has been done at the cost of some tricks, mostly located in the module lea.toolbox. This support has prevented using some advanced Python 3 constructs, especially for method signatures. Python 2. support has been halted since a couple of years, and this is starting to cause some issues, for the least, for keeping the packaging process up-to-date.

The new major version Lea 4 is the opportunity to farewell Python 2’s support. This shall allow modernizing the code at several places and make it more maintainable.

Lea 3.4 shall still be there for Python 2 users, however the branch Lea 3 is not expected to be maintained any longer. At the time of writing, the latest release (Lea 3.4.4) has no open bug. If needed, minor versions could be done for (future) bug fixing.

Note that Lea 4 introduces at least one backward incompatible evolution (see #72).

[Pierre Denis]

This evolution should preferably be made after #71.

[Pierre Denis]

Remove support to Python versions strictly less than v3.5; correct code style, typos (refs #73, #74)

→ <<cset 4dd8d171515e>>

[Pierre Denis]

Fix compatibility issues with Python 3.8- (refs #73)

→ <<cset b45c164f9237>>

[Pierre Denis]

Make Python 3.8 the minimum supported version (refs #73)

→ <<cset 65e8c24d48ea>>

[Pierre Denis]

Fix package classifiers and description (refs #73)

→ <<cset 0cee8a572957>>

[Pierre Denis]

Eventually, it's Python 3.8+.

[Pierre Denis]

Use Python 3 (head, *tail) = iterable' construct (refs #73)

→ <<cset 212f0978b0c5>>

[Pierre Denis]

Use Python 3 (head, *tail) = iterable' construct (refs #73)

→ <<cset d436b7d27620>>

[Pierre Denis]

Use builtin math.isclose function (refs #73)

→ <<cset 719016079b30>>

[Pierre Denis]

Undo (head, *tail) = iterable' constructs because tail is a list instead of a tuple (refs #73)

→ <<cset 68f4df62f7e3>>