* Improve gradle plugin task parsing
Added _gradle and _gradlew as symbolic links to gradle.plugin.zsh,
otherwise the plugin was not properly loaded.
Output from `gradlew tasks --all` is now parsed in two levels,
first we find segments between `------...` and a newline.
Second, all those lines are parsed and cleaned using awk
and added to .gradletasknamecache.
Tested on gradle 2.13, and gradlew 2.14.
* Remove .gradletasknamecache before regenerating it
Remove the .gradletasknamecache file to avoid having an unnecessary
newline at the top of the file when regenerating it.
* Improve gradle task parsing by writing .gradletasknamecache atomically
Previously the .gradletasknamecache file was written line by line inside a parsing loop,
which could cause errors such as half-written cache files if the process was aborted.
This also removes the need of deleting the .gradletasknamecache file before parsing.
