The sheer presence of 'std::gmtime' or 'std::localtime' gives rise to C4996 warnings in Microsofts compilers. Alas, the 'fallback(internal::null<>)'functions containing these library calls are never ADL-picked in the respective 'handle(internal::null<>)' selectors. Therefore hiding the fallbacks from msvc is perfectly fine.

* add make_printf_args and make_wprintf_args to printf.h
add minimal test for make_printf_args and make_wprintf_args to printf-test.cc

renamed the old printf_context template to basic_printf_context_t. the original wish was to rename it basic_printf_context, but that clashed with the name of the inner typedef. this style matches the format_context_t struct.

- #926
- The version of android build results follows latest release(5.2.1)
- Comment for Gradle and its plugin for android
 - `net.fmtlib` package name in the manifest

Recovered Gradle build with latest release (ver. 4.10.2)

TravisCI
- Changed several apt configurations & build steps for Android

AndroidManifest:
- package name: fmt -> org.fmtlib

Gradle:
- Plugin version 3.1.3. Requires Gradle 4.4+
- Removed `x86` (duplicated with `x86_64`)
- `-std=c++17`. Latest NDK(clang7) should support this
- Missing `repositories` configuration

For some reason, the `repositories` config affects to the error:
"Could not find com.android.tools.lint:lint-gradle:26.1.3."

Recovery of Gradle build. 1 of N
Modified several apt configurationss and order of the build

This reverts commit 07200f44 because
the latter doesn't work with virtualenv correctly.