0.3.0

specsolve now requires mathspec 0.2.1. This release breaks one import.

• check(spec, sink=...) is removed. To ask a sink without a solve, call
  build(spec, sources).check(sink). A sink refuses only what the built model
  asks of it.

With mathspec 0.2.1:

• A divisor, a power's base or an exponent may add over parameters, such as
  x / (1 - cost) or (1 + rate) ** years.
• A spec composed from several files with mathspec.merge builds. A fragment
  is refused by name.

Fixes:

• A constant sum that no member reaches at a coordinate adds zero there.
• A cases: region whose value is 0, read through a relation, no longer
  makes the build refuse its rows.

The pull requests since 0.2.1:

• feat(sinks): a built model checks whether a sink takes it without a solve, and check no longer takes a sink (#1806)
• feat: specsolve requires mathspec 0.2.1, where a divisor or a power over parameters may add and a spec may be composed from several files (#1800)
• fix(engine): a constant sum that no member reaches at a coordinate adds zero there rather than leaving a gap (#1801)
• fix(engine): a cased quantity whose otherwise is zero no longer reads as short where it is read through a relation (#1804)
• docs: the tutorials teach in the order a new user needs them, and warm-starting a re-solve has its own how-to guide (#1788)
• docs: a how-to guide chooses a solver or writes the model to a file, and lists the solvers this build has (#1790)
• docs: a how-to guide reads an answer into pandas or xarray (#1789)