Started on project design goals.
Split specification list in sections, with check-boxes in front of each goal.
Revised project goals.
Revised project goals.
Re-phrased project description.
Renamed pair expressions to shadow expressions in project goals.
Renamed shadow expressions to meta expressions in project goals.
Revised specification.

- Changed name of meta expressions back to shadow expressions.
- Changed lambda syntax.
- Conditionals may use shadow expressions to provide a more concise representation.
Added PLISP logo to README file.
Revised project design goals.

- Nil will just be an enumerator named :void.
- Comments will be a special function evaluating into :void.
- Enumerators will be shadow expressions with no primary node.
Added *.sublime* and *.clang-format to .gitignore.
Started on general application structure.
Continued working on the PLISP any-type plisp_node_t, and its subtypes.
Revised project goals.

- Expressions are simply to be called "calls".
- Lambdas take a list of nodes rather than a single node to evaluate.
- Shadow expressions were renamed to fork expressions.
Revised any-type subtypes.

- Re-organized typedefs.
- Lamda's now take list of nodes to be evaluated rather than single expression.
- plisp_function_call_t was renamed plisp_c_function_call_t.
Continued revising any-type subtypes.

- Removed VOID subtype, as it will be represented by plain C NULL.
- Added FORK subtype, which will be used to facilitate was formerly called shadow values.
- Improved documentation.