Add import system

[LunaAmora]

Todo:

• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/15
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/7
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/8
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/13
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/18
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/19
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/16
• https://github.com/HigherOrderCO/Bend-Package-Manager/issues/20
• Finish documentation

closes #514

Current syntax:

# A path starting with `./` or `..` will be imported relative to the file.
# Otherwise, the path will be relative to the folder of the main file.

# imports the `file` top level name from the file.bend, and all other names as 'file/name'
from path import file
import path/file

# imports the listed top level names
from path/file import a
from path/file import (a, b)
import (path/file/a, path/file/b)

# imports all names from the file
from path/file import *

# imports all `.bend` files from the folder
from path import *

# imports the `file` top level name from the file.bend aliased to `alias`, and all other names as 'alias/name'
from path import file as alias
import path/file as alias

# imports the listed top level names, each aliased to a new name
from path/file import a as A
from path/file import (a as A, b as B)
import (path/file/a as A, path/file/b as B)

[developedby]

Can you write some documentation on how to use imports as a user?
With the namespace rules, etc.
It can go in the docs folder.

Also document the syntax on docs/syntax.md and add an entry in the changelog

[LunaAmora]

Can you write some documentation on how to use imports as a user? With the namespace rules, etc. It can go in the docs folder.

Also document the syntax on docs/syntax.md and add an entry in the changelog

What to you mean by namespace rules?

[developedby]

Can you write some documentation on how to use imports as a user? With the namespace rules, etc. It can go in the docs folder.
Also document the syntax on docs/syntax.md and add an entry in the changelog

What to you mean by namespace rules?

I mean how the path search correspond to names, what names are reachable, etc.

[LunaAmora]

@developedby Could you review the docs/imports.md with the new changes? Later i'll finish the rebase so that it can be merged if no further changes are needed.