Added a Travis CI build file.
Added a Travis CI build file.

This allows for continuous integration builds by travis-ci.org.
More information at https://docs.travis-ci.com/user/languages/cpp

bitcoin/leveldb,matehat/leveldb,xuzhezhaozhao/leveldb,yuwolf/leveldb,olzhabay/PMIndexDB,Jianbo-Yang/leveldb,bitcoin/leveldb,zxylvlp/leveldb,tianhuhui/leveldb,zxylvlp/leveldb,bitcoin-core/leveldb,yuwolf/leveldb,WeiHaocheng/LevelDBBuffer,WeiHaocheng/LevelDBBuffer,tianhuhui/leveldb,PFZheng/leveldb,matehat/leveldb,google/leveldb,bitcoin-core/leveldb,Mojang/leveldb-mcpe,olzhabay/PMIndexDB,olzhabay/PMIndexDB,luke-jr/leveldb,cmumford/leveldb,fuchsia-mirror/third_party-leveldb,xuerenlv/leveldb,Mojang/leveldb-mcpe,betterdenger/leveldb,norton/leveldb,WeiHaocheng/LevelDBBuffer,norton/leveldb,fuchsia-mirror/third_party-leveldb,Jianbo-Yang/leveldb,dwing4g/leveldb,xuzhezhaozhao/leveldb,PFZheng/leveldb,luke-jr/leveldb,yuwolf/leveldb,alexxvk/leveldb,yummyliu/leveldb,yummyliu/leveldb,fastogt/leveldb,norton/leveldb,bitcoin-core/leveldb,alexxvk/leveldb,tianhuhui/leveldb,cmumford/leveldb,zxylvlp/leveldb,PFZheng/leveldb,likema/leveldb,yummyliu/leveldb,jacklicn/leveldb,xuerenlv/leveldb,dwing4g/leveldb,fastogt/leveldb,dwing4g/leveldb,xuzhezhaozhao/leveldb,matehat/leveldb,jacklicn/leveldb,betterdenger/leveldb,Mojang/leveldb-mcpe,jacklicn/leveldb,likema/leveldb,google/leveldb,betterdenger/leveldb,bitcoin/leveldb,alexxvk/leveldb,xuerenlv/leveldb,Jianbo-Yang/leveldb