Fix integer parser.

Before this, the number 1234 was parsed as 64 = 10*1 + 10*2 + 10*3
+ 4.
Merge pull request #7 from timjb/fix-integer

Fix integer parser
new example: JSON parser
Switch to continuation-passing-style implementation
JSON parser: use lazy values for recursive parsers
Merge pull request #8 from timjb/cps

Switch to continuation-passing-style implementation
Merge pull request #9 from timjb/json-example

JSON example
Fix typo: "expontent".