New Domain.join() constructor

[saidctb]

Construct a multipatch domain using the new signature where the user can define it as follows:

patches = F0(A), F1(A), F2(A), F3(A)

# Each boundary is identified by a tuple of 3 integers: (patch, axis, ext)
# Each interface is identified by a tuple of 2 boundaries and the orientation: (minus, plus, ornt)
# In 2D ornt is an integer that can take the value of 1 or -1
# In 3D ornt is a tuple of 3 integers that can take the value of 1 or -1
# The connectivity list in 2D
connectivity = [((0, 0, 1), (1, 0, -1),  1),
                ((0, 1, 1), (2, 1, -1),  1),
                ((1, 1, 1), (3, 1, -1), -1),
                ((2, 0, 1), (3, 0, -1), -1)]

# The connectivity list in 3D
connectivity = [((0, 0, 1), (1, 0, -1), ( 1, 1, 1)),
                ((0, 1, 1), (2, 1, -1), ( 1,-1, 1)),
                ((1, 1, 1), (3, 1, -1), (-1, 1,-1)),
                ((2, 0, 1), (3, 0, -1), (-1, 1, 1))]

# Multi-patch domain
Omega = Domain.join(patches=patches, connectivity=connectivity, name='Omega')

The information about the connectivity is based on the format presented in the paper:
T. Dokken, E. Quak, V. Skytt. Requirements from Isogeometric Analysis for changes in product design ontologies, 2010.

[yguclu]

Does this PR solve issue #108?

[saidctb]

Does this PR solve issue #108?

yes

[yguclu]

Does this PR solve issue #108?

yes

That's great! Please add a short description to this PR.

[yguclu]

This looks very good @saidctb!

Could you add an example/test in 3D?

Further, have you checked if we are now able to connect two patches with more than one interface?

[saidctb]

This looks very good @saidctb!

Could you add an example/test in 3D?

Further, have you checked if we are now able to connect two patches with more than one interface?

yes, we now can connect two patches with two interfaces

[saidctb]

This looks very good @saidctb!

Could you add an example/test in 3D?

Further, have you checked if we are now able to connect two patches with more than one interface?

the 3D test was added in bb148fe

[yguclu]

Great job @saidctb!

I have some minor comments.