Parameter transformer

[zihaoxu98]

This PR adds a new class called Transformer which applies transformation of the parameters. Some of the previous code is slightly modified but should not interfere any previous code.

To define a transformer, you need to specify its 1. domain 2. codomain 3. transform (domain to codomain) and inverse transform (codomain to domain) 4. Jacobian. In principle everything should already be defined by giving transform, however we will rely on the users to define the symbolic inverse transform and Jacobian. The Jacobian is needed to transform the log posterior pdf. An example is also added to the test.

The Transformer can act on almost all appletree classes by simply doing something like

transformer = TestTransformer()
transformed_obj = transformer(obj)

where obj can be 1. a dictionary of parameters 2. apt.Parameter 3. apt.Component 4. apt.Likelihood 5. apt.Context

[coveralls]

Pull Request Test Coverage Report for Build 8289067506

Details

• 146 of 186 (78.49%) changed or added relevant lines in 6 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.5%) to 84.613%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
appletree/parameter.py	10	14	71.43%
appletree/component.py	13	21	61.9%
appletree/transform.py	117	145	80.69%

Files with Coverage Reduction	New Missed Lines	%
appletree/parameter.py	3	86.86%

Totals
Change from base Build 8190832365:	-0.5%
Covered Lines:	2403
Relevant Lines:	2840

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💛 - Coveralls

[dachengx]

Thanks @zihaoxu98 . This PR is gorgeous, but maybe appletree currently does not strongly need it. I will convert it to draft and if we need it we can come back in the future.