Rename macros

[Emoun]

Short Description:

Rename the macros:
duplicate_inline -> duplicate (new),
duplicate(old) -> duplicate_item.

Motivation:

#28 decided that duplicate_inline would be used in nested substitution.
Therefore, the current name is a bit long for something that would probably be embedded inside other code.
duplicate(old) on the other hand is often on its own, or as part of shorter lines, so giving it a longer name wouldn't be an issue.

duplicate_inline is also the more general of the macros (everywhere can use duplicate(old) you can also use duplicate_inline, but not vice versa).
Therefore, if it has the shorter name, new users trying it out (without knowing the difference) would have faster success.

Design

Simple rename.

Misc:

Initially, we will simply rename everything in the documentation. However, since duplicate_inline will become the new default macro, we might want to refocus the documentation to account for this.

[Emoun]

To avoid confusion between the names. Any future github issues should use the new names.
However, the commit history should stick to the old names until the rename is implemented, after which it should switch.

[Emoun]

Implemented awaiting next release