Initial commit
Merge branch 'master' of https://github.com/penglin03/sicp-answers
Add ex1.1.txt.
Add ex1.2.
Add ex1.3.
Add ex1.4.
Add ex1.5.
Add examples in textbook for practice.
Add examples.c.
Add ex1.6.txt.
Add ex1.8.scm.
Add ex1.7.
Add ex1.9.txt.
Add ex1.10.txt.
Add ex1.11.scm.
Add ex1.11.c.
Add ex1.12.scm.