provide targets for building native extensions during CrossBuild

Alloc doc

Mrb string value cstr patch

Need mruby-compiler to build mruby-bin-mruby and mruby-bin-mirb for

Proc#curry should preserve lambdas

cross compiles

From the CRuby 2.2.2 Proc#arity documentation:

If the block has optional arguments, returns -n-1, where n is the number
of mandatory arguments, with the exception for blocks that are not
lambdas and have only a finite number of optional arguments; in this
latter case, returns n.

Add :mgem gem loading.

Fix repository link to mruby/mruby

Fix typos in documentation and error messages

[ci skip] Remove some Srting#split samples

mruby not support regexp, so remove these samples.

Time rounding precision

refactor code to call mrb_inspect() instead

mrb_inspect() also calls mrb_obj_as_string() after #inspect to ensure
the mrb_value is a string.

Remove the unused libterminfo detection code.

The detection code is unused even on OpenBSD 5.7,
because of the standard installation is libtermcap be installed, not libterminfo.

This fixes #2829

Tested on Arch Linux (x86_64) & OpenBSD 5.7 (amd64).
Signed-off-by: Huei-Horng Yo <hiroshi@ghostsinthelab.org>

Detect if ncurses' backend is terminfo or termcap.

Borrowed from @mattn's code at:
https://github.com/mruby/mruby/issues/2662#issuecomment-65535705Signed-off-by: Huei-Horng Yo <hiroshi@ghostsinthelab.org>

gsub/sub supports back references in substitutes.  fixes #2816.