Update SQLite plugin details

[nikhilkh]

@brodybits to help review.

[brody4hire]

I don't think "relies on native SQLite implementation" is so relevant anymore. The cordova-sqlite-storage version now includes its own sqlite3 implementation. Also yours truly (@brodybits) broke the cordova-sqlite-storage README link.

For the README links, would it be an idea to consider using "#readme" at the end of the repo link instead of hardcoding the link through the default branch name?

FYI other changes may be coming:

• An "express-core" version that would use the built-in sqlite libraries for Android and iOS (not sure if we should really link this)
• The default branch of the SQLCipher version (for which there is no link) will probably change
• I may move or rename the "evfree" version.

In the past I would maintain the plugin source code in separate branches and publish a "*-master" branch that would also include the sqlite3 source/library dependencies. I changed cordova-sqlite-storage and cordova-sqlite-ext to fetch the sqlite3 source/library dependencies from npm (as discussed in apache/cordova-discuss#38) and published them from lighter-weight branches. I expect to do the same for the SQLCipher and "evfree" versions.

[brody4hire]

The updates look good to me, thanks!

FYI I dropped the Cordova engine constraint on Cordova-sqlite-storage.