Adopt for AUR 3.0 release

Use makepkg to build source package.

Handle prerelease dependencies

If the dependency is for prerelease then use prerelease gem index for it.
prerelease package always creates a versioned package.

README.md: Fix several grammatical, spelling, and capitalization errors

This also brings the help text (program options) closer in line with
that from 'gem2arch --help'.

Generate correct full version for versioned packages

Merge gembump into gem2arch script

Unify warning messages

source url - use https and avoid quoting

Carry license from exisint PKGBUILD

Many gemfiles do not provide license. So we should read it from the existing one and use it during generation.

Fix a bug when gem2arch actually generated PKGBUILD for one of the dependencies.

Move find_license_file functionality to a separate function

gem2arch version 0.2

- various code cleanup and simplification
- output PKGBUILD simplification
- add GPL3 license to gem2arch project
- if gem has a license install it during Arch package installation
- fix license=(), we need to use metadata from the gem file

Signed-off-by: Anatol Pomozov <[email protected]>