Add component-list constructors and cross-philosophy conversions

- Change single-real constructor in "complex_it" to take a list of
  components instead.
- Add component-list constructor to "complex_rt" (recursive case).
- Add constructor and operator (both explicit) in "complex_rt" (both
  cases) for converting to or from "complex_it."  (This is a
  prerequisite for the previous item.)
- Remove some verbiage from the old constructors in "complex_rt"
  (recursive case).
- Correct some spelling errors.