- persistence.cpp code expects special sizeof value for passed structures
- this assumption is lead to memory corruption problems
- fixed/workarounded test to prevent memory corruption on Linux 32-bit systems

create a dummy gzFile type

the "std::basic_ios::operator bool" differs between C++98 and C++11. The
"double not" syntax is portable and covers both cases with equivalent
meaning

Append zero to trailing decimal place for FileStorage JSON write of a float or double value (#7952)

* Fix for FileStorage JSON write of a float or double value that has no fractional part; appends a zero character after the trailing decimal place to meet JSON standard.

* strlen return to size_t type rather than unnecessary cast to int

In YAML 1.0 the colon is mandatory. See http://yaml.org/spec/1.0/#id2558635.

This also allows prior releases to read YAML files created with the current version.

- one test for type_id;
- another for comments in JSON;

a JSON emitter, a parser, tests and some basic doc.

- use `std::string` instead of `new char`;
- reserve 1 MB for buffer;

- use `@snippet` instead of `@code` in docs.
- remove some functions that were not used.

Modified performance test and solve a problem caused by an enum type.

Major changes:

- modify the Base64 functions to compatible with `cvWriteRawData` and so
on.
- add a Base64 flag for FileStorage and outputs raw data in Base64
automatically.
- complete all  testing and documentation.

The three new functions:

```cpp
void cvStartWriteRawData_Base64(::CvFileStorage * fs, const char* name,
int len, const char* dt);
void cvWriteRawData_Base64(::CvFileStorage *
fs, const void* _data, int len);
void
cvEndWriteRawData_Base64(::CvFileStorage * fs);
```

Test is also updated. (And it's remarkable that there is a bug in
`cvWriteReadData`.)

```cpp
cvWriteMat_Base64(::cv::FileStorage & fs, ::cv::String const & name,
::cv::Mat const & mat)
```
becomes:
```cpp
CV_EXPORTS void cvWriteMat_Base64(::CvFileStorage* fs, const char* name,
const ::CvMat* mat);
CV_EXPORTS void
cvWriteMatND_Base64(::CvFileStorage* fs, const char* name, const
::CvMatND* mat);
```

Two test are still needed:

1. Verify the Base64 data.
2. Read an old YML file for compatibility test.

Two other test are still needed.

1. Verify the Base64 data.
2. Read an old YML file for compatibility test.

[GSoC] FileStorage:
Add base64 support for reading and writting XML\YML file.
The two new functions:
```
void cvWriteRawData_Base64(cv::FileStorage & fs, const void* _data, int
len, const char* dt);
void cvWriteMat_Base64(cv::FileStorage & fs, cv::String const & name,
cv::Mat const & mat);
```

at least it is possible to read/ write calibration files. Fixes #4282.

Also add CPP method for writing comments.