Made parser capable of handling USEMINSPACING and MASKS in rectangles

[DavidAguilo]

Needed to handle these 2 keywords for a project, thought I might as well contribute.

[dan-fritchman]

Awesome thanks!

[dan-fritchman]

Sorry but this was failing to build and/or test, and had to be reverted via #46.

   Compiling layout21raw v3.0.0-pre.3 (/Users/dan/dev/Vlsir/Layout21/layout21raw)
error[E0308]: `?` operator has incompatible types
   --> layout21raw/src/lef.rs:136:39
    |
136 | ...21::LefShape::Rect(self.export_point(&r.p0)?, self.export_point(&r.p1)?)
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `Option<Decimal>`, found `LefPoint`
    |
    = note: `?` operator cannot convert from `LefPoint` to `std::option::Option<rust_decimal::decimal::Decimal>`
    = note: expected enum `std::option::Option<rust_decimal::decimal::Decimal>`
             found struct `LefPoint`

error[E0061]: this enum variant takes 3 arguments but 2 arguments were supplied
   --> layout21raw/src/lef.rs:136:17
    |
136 | ...   lef21::LefShape::Rect(self.export_point(&r.p0)?, self.export_point(&r.p1)?)
    |       ^^^^^^^^^^^^^^^^^^^^^------------------------------------------------------ an argument of type `LefPoint` is missing
    |
note: tuple variant defined here
   --> /Users/dan/dev/Vlsir/Layout21/lef21/src/data.rs:429:5
    |
429 |     Rect(Option<LefDecimal>, LefPoint, LefPoint),
    |     ^^^^
help: provide the argument
    |
136 |                 lef21::LefShape::Rect(self.export_point(&r.p0)?, self.export_point(&r.p1)?, /* LefPoint */)
    |                                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error[E0023]: this pattern has 2 fields, but the corresponding tuple variant has 3 fields
   --> layout21raw/src/lef.rs:382:18
    |
382 |             Rect(ref p0, ref p1) => self.import_rect((p0, p1)),
    |                  ^^^^^^  ^^^^^^ expected 3 fields, found 2
    |
   ::: /Users/dan/dev/Vlsir/Layout21/lef21/src/data.rs:429:10
    |
429 |     Rect(Option<LefDecimal>, LefPoint, LefPoint),
    |          ------------------  --------  -------- tuple variant has 3 fields
    |
help: use `_` to explicitly ignore each field
    |
382 |             Rect(ref p0, ref p1, _) => self.import_rect((p0, p1)),
    |                                +++

@DavidAguilo do you want to make some updates and we can roll it back in?

[DavidAguilo]

Ok, I'll take a look at it. I guess changing the Rect struct made it necessary to change the tests as well. Oh and layout21.