Ch. 1: 5 is a number not a symbol

Use the symbol `foo' instead.
Ch. 2: Fix docstrings and message

Use proper docstring format, and make the message consistent with the
examples.

Interactive commands don't need to return values.   Besides, `progn' is
introduced much later in chapter 8.
Ch. 4: Fix doc strings and string changes

Add a doc string to `buffer-exists-p' and add buffer name to message.

Add `RET' to find-tag solution.
Ch. 5: wenshan-compare-with-fill-column

Add docstring.
Improve message to user.
Fix logic so that it really compares with 56 by default -- was comparing
1.
Ch. 6: Remove save-excursion
Ch. 7: Show results of modifying lists
Ch. 8: Change search prompt and variable name
Ch. 9: Fix typo and show result of list modification
Ch. 10: Use arithmetic to see how many blocks left
Ch. 11: Fix docstrings and rewrite exercise 4
Ch. 12: Use newline escape sequence
Ch. 13: Fix typo
Ch. 15: Prefix functions and give example output
Added `contributors' in README