The current deserialization feature detects wrong scalar value types from token in some valid floating point value formats which contain the decimal point and/or the exponent:

• the significand is an integer before the exponent (reported in the issue Bug on parinsing trivial YAML #413)

  1e-1

• the significand's integer part is omitted

  - .1e+2
  - -.1e-1
  - .1e2

• the significand's fractional part is omitted

  - 1.e2
  - -1.e-1
  - -1.e+2

• the significand is 0

  0e+1

All of them are valid according to the YAML standard 1.2, but the scalar_scanner class mistakenly detects them as either integer or string scalar value types.

This PR fixes such wrong detections and a number of test cases are also added to validate the changes.

Pull Request Checklist

Read the CONTRIBUTING.md file for detailed information.

• Changes are described in the pull request or in a referenced issue.
• The test suite compiles and runs without any error.
• The code coverage on your branch is 100%.
• The documentation is updated if you added/changed a feature.

Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
• Please refrain from proposing changes that would break YAML specifications. If you propose a conformant extension of YAML to be supported by the library, please motivate this extension.
• Please do not open pull requests that address multiple issues.