Improve function naming consistency.

[vitaut]

Currently there is an inconsistency in function naming. Some functions are named according to Google C++ Style Guide:

• Format
• Print
• Clear
• ReportSystemError
  ...

Other follow standard library conventions:

• c_str
• str
• clear
• resize
• reserve
• printf
• sprintf
  ...

The names should be unified before the version 1.0 of the API is released. This is pretty arbitrary, but it's probably better to follow standard library conventions for public API for consistency with printf and because its done already for most functions.

[vitaut]

To minimize the number of API changes, it might be useful to consider simplification of a common use case of formatting into an std::string here too. Currently it requires two function calls:

str(Format("{}", 42));

Ideally it should require a single function call. Possible ways to do this:

1. Make format return std::string.
2. Add another method (strformat) returning std::string.

[vitaut]

Fixed in version 0.9.0.