Remmappings to the foundry file

[mario-eth]

Currently, the remappings are added to the remappings.txt file.
There should be a way to add them to the foundry.toml config under the remappings.

[ZeroEkkusu]

Not directly related, but installing a new dependency regenerates all remappings (which are in remapping.txt currently).

For example, when Forge Std is installed it generates:

@forge-std-1.9.1=dependencies/forge-std-1.9.1

But let's say I change it to:

@forge-std=dependencies/forge-std-1.9.1/src

Now, when I install a next dependency, it will come back:

@forge-std=dependencies/forge-std-1.9.1/src
@forge-std-1.9.1=dependencies/forge-std-1.9.1
@next-dependency-1.0.0=dependencies/next-dependency-1.0.0

It would be nicer if it only appended new remappings, and not regenerated all.

[mario-eth]

Issue developed here #112