Backport recent features

The [main repository](https://github.com/JetBrains/intellij-plugins/tree/master/handlebars) is now targeting IDEA 14+ based products, so backport some recent features (specifically [subexpression support](https://github.com/dmarcotte/intellij-plugins/commit/e12920b758c8986827503b32c4b59b84c93490c6#diff-b644d7b7e647851e177e6d311c1a185d) and [decimal support](https://github.com/dmarcotte/intellij-plugins/commit/caeef17ef82b0037eadedadfaa04c8685eb1a018#diff-b644d7b7e647851e177e6d311c1a185d)) for a release targeting IDEA 12/13 based products.