contracts: Adding contents(#1419)

## Sections to do
- 3.4.5 Objects Passed and Returned in Registers
- 3.4.6 Not Part of the Immediate Context
- 3.4.7 Function-Template Specializations
- 3.4.8 No Implicit Lambda Captures
- 3.5.11 Mixed Mode
- 3.6.1 Undefined Behavior During Contract Checking
- 3.6.2 Invalid Data Member Access in Constructors and Destructors
- 3.6.3 Friend Declarations Inside Templates
- 3.6.4 Recursive Contract Violations
- 3.6.5 Concurrent Contract Violations
- 3.6.6 Throwing Violation Handlers (detailed version)
- 3.6.7 Differences Between Contract Assertions and the assert Macro
(complete version)

Author: rotarymars